
Class 

Book 






GopyrigM . 



COPYRIGHT DEPOSIT, 



COMMERCIAL ENGINEERING 

FOR 

CENTRAL STATIONS 



Published by the' 

McGraw-Hill BookCompany 

New Voirk 

6ucce£sor« to theBookDepartments of tke 

McGraw Publishing Company Hill Publishing" Company- 

Publishers of Books for 
Electrical World The Engineering and Mining Journal 

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r/AAAAAAfiAf^ttflstf.Atf^fiAf.Ai 



COMMERCIAL ENGINEERING 

FOR 

CENTRAL STATIONS 



A COMPILATION OF PAPERS DEALING WITH SUBJECTS 

OF PARTICULAR INTEREST TO THOSE ENGAGED 

IN CENTRAL STATION COMMERCIAL 

ENGINEERING WORK 



BY 
ARTHUR WILLIAMS 

PAST-PRESIDENT NATIONAL ELECTRIC LIGHT 

ASSOCIATION, MEMBER OF THE AMERICAN 

INSTITUTE OF ELECTRICAL ENGINEERS 

AND 

EDMUND F. TWEEDY 

COMMERCIAL ENGINEER 



McGRAW-HILL BOOK COMPANY 

239 WEST 39TH STREET, NEW YORK 

6 BOUVERIE STREET, LONDON, E. C. 

1912 



^ 



^ 



Copyright, 1912 

BY THE 

McGraw-Hill Book Company 






THE. MAPLE. PRESS- TOEK. PA 



Ml 

CCI.A314910 



INTRODUCTION 

The several chapters of this book deal with a number of 
subjects more or less diverse in character. The compilation 
of these different subjects in one book can, perhaps, be justified 
upon the ground that they all fall within the scope of central 
station commercial engineering. A few of the chapters — in 
slightly different form — have appeared in certain of the tech- 
nical periodicals during the past year, notably in Power and in 
the Electrical World; the subject-matter contained in the re- 
maining chapters makes its initial appearance in this book. 
The various data embodied in this compilation of papers have 
been accumulated by the authors while conducting investiga- 
tions along commercial engineering lines for one of the largest 
central stations. "^ 

As an aid in widening the field of application for their product, 
the importance of commercial engineering is becoming more 
generally recognized by the central stations as they proceed 
further into the industrial field in search of a market for their 
output. The responsibility of discovering new applications for 
the use of electrical energy rests, therefore, largely with the 
commercial engineer, upon whom also devolves the respon- 
sibility of thoroughly investigating and analyzing existing 
applications of electrical energy, to the end that accurate oper- 
ating data may be secured, that all possible economies may be 
effected, and that the public may be furnished with a useful and 
convenient service. 

The Authors. 



/ 



CONTENTS 

Page 
CHAPTER I 

Estimating the amount of coal required to heat a modern city building . 1 

CHAPTER II 
Cooling the air of buildings by means of mechanical refrigeration . . . 14 

CHAPTER III 
Mechanical refrigeration for the cold storage of furs and fabrics .... 26 

CHAPTER IV 
The application of mechanical refrigeration to ice cream making. . . 35 

CHAPTER V 
Cost of generating electrical energy in steam driven central stations of 

small and medium size 49 

CHAPTER VI 
Kilowatt hour costs in steam-driven generating plants 54 

CHAPTER VII ( 
Central station load factors 69 

CHAPTER VIII 
Electricity in the modern department store 77 

CHAPTER IX 
The passenger elevator in office building service 88 

CHAPTER X 
Ozone: Its production and utilization 103 

CHAPTER XI 
The use of electricity for the disinfection of sewage .117 



COMMERCIAL ENGINEERING FOR 
CENTRAL STATIONS 



CHAPTER I 

ESTIMATING THE AMOUNT OF COAL REQUIRED TO HEAT 
A MQDERN CITY BUILDING 1 

The artificial heating of all habitable buildings throughout 
the greater part of the temperate zone is necessary during some 
6 to 8 months of the year, if inside temperatures conducive to 
the physical comfort of those who reside within are to be 
maintained. 




Oct. Nov. Dec. Jan. Feb. Mar. Apr. May 

Fig. 1. — Showing the relative heating requirements of several different 
cities of the United States, based upon mean monthly temperatures. 

Some idea of the relative importance of this heating problem 
in different sections of our own country may be obtained by 
referring to Fig. 1 , which shows the mean monthly temperatures 
in a number of cities located in various parts of the United 
States. 

1 This chapter first appeared as an article in Power, Vol. 35, p. 87. 

1 



2 ENGINEERING FOR CENTRAL STATIONS 

This chart is based upon the assumption that artificial heating 
is required when the mean outside temperature is below 55° F., 
and that the amount so required is proportional to the difference 
between 70° F. (the assumed inside temperature) and the mean 
outside temperature. The mean temperature for a given month 
is plotted upon a vertical line erected at the middle point of the 
corresponding month. Straight lines are drawn between the 
various points thus obtained, and from the two points where the 
horizontal line through 55° F. is crossed, vertical lines are 
erected to meet a horizontal line drawn through 70° F. The 
areas of the polygons thus obtained roughly represent the heat- 
ing requirements in the several cities which have been selected 
for comparison. The intercepts upon the horizontal line drawn 
through 55° F. give an approximate idea of the number of days 
comprising the heating season, for each city. The accompany- 
ing table, No. 1, gives the mean monthly temperatures of these 
several cities, as well as the mean temperatures during the 
heating season and the number of days during which heating is 
required, both of the latter sets of figures being obtained from 
Fig. 1. The last line of this table gives the heating require- 
ments of each of these cities as a percentage of those of New 
York City. In determining these relations, however, no allow- 
ance has been made for any differences in mean wind velocity, 
although this is a factor which may materially affect the heating 
requirements, as is shown later on. Furthermore, they make 
no allowance for those days, if any, during the heating season 
when either no, or only a small amount of, heating may be 
required, such as on Sundays, holidays, etc., and they therefore 
do not afford an accurate means of comparing the heating 
requirements of two given buildings located in different cities, 
if the operating conditions of these buildings, as regards con- 
tinuity of heating, are radically different. 

The loss of heat by transmission through the various materials 
of which modern buildings are composed, has been made the 
subject of much experimental study, and, as a result of the many 
investigations which have been made along these lines, it is now 
possible to predict, with a considerable degree of accuracy, the 
loss of heat which any given building will experience by trans- 
mission through its walls, roof, etc., for any given conditions as 
regards building exposures and outside and inside temperatures, 
when the nature of the materials of which the building is con- 



AMOUNT OF COAL REQUIRED 



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4 ENGINEERING FOR CENTRAL STATIONS 

structed, together with the thicknesses of such materials, is 
definitely known. 

Table No. 2, compiled from data given by various authorities, 
shows the approximate amount of heat that is transmitted per 
square foot per hour for every degree difference in temperature 
between the inside and outside air for a few of the materials 
most commonly used in the construction of modern city build- 
ings. The heat losses as given in this table are, when used as a 
basis for calculating the amount of radiating surface required, 
generally increased by some 10 to 20 per cent, when the exposure 
is a northerly one; by 10 to 30 per cent, when the building is 
heated during the daytime only, the percentage of increase 
depending upon whether the building is in a protected or in an 
exposed location, and by 50 per cent, when the building is heated 
only intermittently, with intervals of considerable duration 
when the building is without heat. 

TABLE NO. 2 

Brick Walls 

Thickness in inches 8 12 16 20 24 30 36 

B. T. U. loss per square foot per 

hour per degree difference in 

temperature 46 .32 .26 .23 .20 .17 .13 

Stone Walls (Sandsto?ie) 

Thickness in inches 12 16 20 24 28 36 44 

B. T. U. loss per square foot per 

hour per degree difference in 

temperature 44 .38 .36 .30 .27 .24 .20 

B. T. U. loss per square foot 

per hour per degree 

difference in temperature 

Single window 1 . 03-1 . 1 

Double window . 45- . 52 

Single skylight 1 .00-1 . 14 

Double skylight .62 

The loss of heat occasioned by the leakage of air at the windows 
and doors is, however, not subject to precise calculation, and 
this loss may result in an insufficient amount of radiating surface 
being provided, unless proper allowance is made to cover this 
loss, either by basing the estimate upon previous experience or 



AMOUNT OF COAL REQUIRED 5 

by following one of the more or less empirical methods that are 
frequently used in providing for the loss of heat due to this 
cause. The most common method of making provision for this 
loss is to assume an arbitrary number of air changes per hour 
for that portion of the building which is to be heated, but this 
method is uncertain at best and it may lead to considerable 
error. 

In order to eliminate the uncertainty that arises from esti- 
mating the heat loss due to air leakage by assuming an arbitrary 
number of air changes per hour, the authors employ a method 
which combines this loss with the heat loss due to transmission, 
both being expressed in terms of equivalent glass. The possi- 
bility of making such a combination was arrived at by the follow- 
ing line of reasoning: The loss due to air leakage is proportional 
to the summation of the window perimeters (assuming the 
leakage space around the windows to be approximately constant 
in width) , but as the dimensions of the windows in similar types 
of city buildings are fairly uniform, it becomes possible to con- 
sider the leakage loss as a function of the total window glass sur- 
face, when deriving a general expression for the loss of heat from 
buildings of a given type, without introducing any considerable 
amount of error. 

In reducing wall exposure to equivalent glass, a ratio of 4.5 to 
1 has been taken as representing the relation which the heat 
transmitting properties of glass bear to those of the materials 
of which the walls of the average building in New York City are 
constructed. Having made the foregoing assumptions, the 
following equation results: 

W 

K ^K f 

T =Tons of coal consumed per year for heating. 
W = Total exposed wall surface in square feet. 
G = Total window glass surface in square feet. 
K and K' = Constants for buildings of the same type and of 
similar form of construction. 

As it is not necessary to solve the above equation, K and K f 
need not be separately determined. However, in order to 
provide a relation between the actual coal consumptions and 
the total glass equivalents of the buildings that were investi- 



ENGINEERING FOR CENTRAL STATIONS 



gated, it was necessary to express K' in terms of K. 
the equation evidently becomes 

W 



YorK' = K. 



4.5 



+2G 



K 

The relation between K and K! can be varied considerably, 
however, without affecting the result to any appreciable extent 
other than to alter the value of K. 

Fig. 2 shows the results obtained by plotting the actual yearly 
coal consumptions of some 18 office and loft buildings located 
in New York City, against the total glass equivalents of these 



800 



400 



o 
2 200 



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Fig. 2. 



10,000 20,000 30,000 40,000 50,000 60,000 
Value of ^+2G (=Sx 2 Approximately) 

-Showing the relation between the total glass equivalent and the 
tons of coal required per year for heating. 



buildings, as represented by the numerator of the quantity on the 
right-hand side of the equation given above. The coal consumed 
in these buildings was used for heating purposes only, as all 
light and power requirements are supplied by means of electrical 
energy purchased from the central station. The loft buildings 
that are included are not what are known as manufacturing lofts, 
but they are, for the most part, devoted solely to sales purposes. 
It will be observed that the value of K for this type of building 
is approximately 100, which is a very convenient figure for 
practical use. Pea coal was used in almost all of the buildings 
which appear on this chart, but data were secured on a number 
of buildings where the buckwheat coals, or various mixtures, 
were being used. All such cases — as would naturally be expected 



AMOUNT OF COAL REQUIRED 7 

from the somewhat lower average calorific value of such fuels — 
fall above the average of the buildings using pea coal, but m 
some cases to a considerably greater extent than can readily 
be explained by the difference in the thermal values of the fuels. 
This divergence, however, can undoubtedly be accounted for 
by the fact that these poorer grades of fuel are rarely burned 
under proper conditions as regards type of grate and amount of 
draft. However, if properly burned and if of reasonably good 
quality, these fuels show a fairly close relation between the total 
glass equivalent and the number of tons consumed. For other 
types of buildings the same relation has been found to hold 
good, the only difference being a variation in the constant, K. 
For instance, in the case of apartment houses it has been found 
that the same equation may be employed, provided K is given 
a value of about 60, instead of 100. In other words, apartment 
houses, for the same total glass equivalent, consume more coal 
for heating than do office or loft buildings. This is, of course, 
due to the fact that apartment houses require heat during more 
hours of the day than does the average commercial building. 
In addition to this the windows are generally opened consider- 
ably more in apartment houses and these buildings are usually 
of a poorer type of construction than modern office and loft 
buildings. This latter condition, however, may be offset by 
the increased air leakage loss due to the greater height of the 
average modern commercial building. 

In examining the chart shown in Fig. 2, it will be observed 
that only four of the buildings show any appreciable amount of 
divergence from the mean, as represented by K = 100. The 
divergence of these four cases can be readily explained. One of 
those falling below the line was due to a considerable portion of 
the building being vacant and only being partially heated; the 
other is a building where a considerable amount of heat results 
from the industrial use to which a portion of the building is 
devoted. The two cases above the line are due, respectively, 
to poor building construction and to inefficient operation of the 
heating plant. 

The foregoing explanation of the methods that were followed 
in deriving the equation upon which this chart is based, will 
make it evident that this equation cannot be employed with 
any high degree of accuracy in the case of any building that 
is so peculiar in its construction as to widely differentiate it 



8 ENGINEERING FOR CENTRAL STATIONS 

from others of its class; also, where mechanical ventilation is 
to be employed, a certain allowance must be made for the loss 
of heat arising from this source, over and above that which the 
equation provides for in the form of natural ventilation due to 
air leakage. However, as a means of estimating the amount of 
coal required to heat a given building, the authors have found 
this method to be of considerable value, and, owing to the many- 
uncertainties that are invariably present in any heating problem, 
the use of this method will probably lead to results quite as 
accurate, in the average case, as those secured by the use of a 
much more involved and elaborate method of calculation. 

A method of estimating the amount of coal required to heat a 
given building, as employed by a Chicago company that is 
engaged in the business of operating steam-heating plants, will 
be briefly outlined. This company has derived a formula based 
upon a heating season extending from October 1 to May 1, a 
total of 243 days, or 5832 hours. The average outside tempera- 
ture during this period being 36° F., the average difference be- 
tween this mean outside temperature and an inside temperature 
of 70° F., is 34°. The amount of heat lost by transmission per 
square foot of glass per hour per degree difference in temperature 
is taken as 2 B. T. TJ., which is twice the amount usually allowed 
for this loss. The loss of heat by transmission through ordinary 
brick or tile wall is taken as one-tenth of the loss through glass, 
or .2 B. T. U. per hour per square foot per degree difference in 
temperature. Taking the number of heat units in a pound of 
steam as 1000, the following equation is obtained: 

n 5X2X34X5832 5X0.2 . 

C = 1000X^X2000 = ~r (^proximately). 

S = Glass surface, plus one-tenth the wall surface (north and 
west exposures being increased 10 per cent.). 

e = Number of pounds of water evaporated per pound of coal. 
C = Tons of coal required for heating. 
It will be observed that S in the above equation is equivalent 

to— ; + G, which may be written in the form l/2l-^- + 2Gj . In 

this latter form the quantity within the parentheses is practic- 
ally identical with the quantity representing the total glass 
equivalent as given previously in the equation developed by the 
authors. The quantity Sx2 in the Chicago equation is, there- 
of 
fore, practically equivalent to the quantity, -r-£-+ 2G in the 

4.0 



AMOUNT OF COAL REQUIRED 9 

authors' equation. In other words, the leakage loss in Chicago 

has been provided for by doubling the glass transmission factor. 

In Fig. 2 the number of tons of coal required for heating have 

W 
been plotted against the quantity —^ + 2G (which is practically 

equivalent to the quantity Sx2 of the Chicago equation) for a 
number of commercial buildings located in Chicago, and it will 
be observed that these buildings fall fairly closely along a line for 
which the value of K is 50. In other words, the amount of coal 
required to heat a building with a given total exposure expressed 
in terms of equivalent glass, is apparently twice as great under 
Chicago conditions as under those existing in New York City, 
the value of K for buildings of a similar type located in the latter 
city having been found to be approximately 100. The question 
naturally arises, how is this observed difference to be reconciled 
with the apparent difference in the heating requirements of the 
two cities as shown in Table 1 ? From this table it would appear 
that the heating requirements in Chicago are approximately 
19 per cent, in excess of those existing in New York City, while 
the actual coal requirements are practically 100 per cent, greater 
in the former city than in the latter. This apparent discrepancy 
can undoubtedly be explained by taking two additional factors 
into consideration — one of which has a very material bearing 
upon the heat loss of a building with a given exposure, while the 
other has an improtant bearing upon the amount of coal required 
to offset a given loss of heat. The first of these factors is that 
of wind velocity; the second is that of evaporation, or the 
average number of pounds of water evaporated into steam per 
pound of coal. 

The average velocity of the wind during the heating season 
in Chicago is a little over 18 miles per hour, while the average 
wind velocity in New York City during the months when heating 
is required is approximately 13 miles per hour. As the wind 
pressure varies approximately as the square of the wind velocity, 
the mean wind pressure during the heating season in Chicago 
is approximately twice that existing in New York City. Now 
the loss of heat by air leakage is naturally a function of the 
mean external air pressure that results from the velocity of the 
wind. Therefore, in order to show the effect which the higher 
average velocity of the wind in Chicago has upon the heating- 
requirements of the buildings in that city, as compared with 



10 ENGINEERING FOR CENTRAL STATIONS 

those of similar buildings in New York City where the average 
wind velocity is considerably lower, it is only necessary to esti- 
mate approximately the average relation of the heat loss due to 
leakage to the total heat loss under New York City conditions. 
In the latter city it has been found that the square feet of 
window surface of office and loft buildings averages about 20 per 
cent, of the total exposed wall and glass surface; hence, by 

W 
referring to the expression for the total heat loss, -. — = + 2G, it 

4. o 

will be seen that the average heat loss from leakage, under New 

York City conditions, is approximately 35 per cent, of the total 

heat loss. Based upon the increased air leakage alone, the 

Chicago heating requirements are therefore 135 per cent, of 

those existing in New York City. 

From tests made upon a vast number of Illinois coals by the 
U. S. Geological Survey, it would appear that a figure of 11,000 
B. T. U. per pound may be taken as representing the average 
heat content of these coals as fired. Pea coal, such as is used 
in the majority of New York City buildings, will probably aver- 
age something over 12,000 B. T. U. per pound. Consequently 
if these different kinds of coal were burned with equal efficiency, 
the amount of Illinois coal required would be about 110 per cent, 
of the amount of pea coal necessary to supply an equal quantity 
of heat. It is very probable, however, that the actual ratio is 
more nearly expressed by 125 per cent., due to the fact that pea 
coal, when used in the average heating plant, will unquestion- 
ably show a considerably higher efficiency than that shown by 
such grades of soft coal as are commonly used in the heating 
plants of Chicago. Hence, if this contention and the foregoing 
assumptions are correct, we have an explanation of the fact that 
the amount of coal required in Chicago for heating a given build- 
ing is twice what it would be were the building located in New 
York City; for 1.19x1.35X1.25 = 2. 

The heating requirements of a large number of Boston build- 
ings have received careful investigation at the hands of Mr. 
Davis S. Boyden of The Edison Electric Illuminating Company 
of Boston, and as a result of these investigations he has developed 
a somewhat complicated formula for use in determining the 
amount of coal required to heat a given building. As the 
accuracy of this formula depends very largely upon what values 
are assigned to a number of variables, its use is necessarily con- 



AMOUNT OF COAL REQUIRED 11 

fined to those who possess more than an ordinary knowledge 
of the subjeet of heating and who are capable of using a consider- 
able amount of judgment in assigning proper values to these 
variables for any particular case. 

In deriving this formula, the assumption is first made that 
1 B. T. U. will raise 55 cu. ft., of air 1° F., from which it follows 
that the heat units lost from a building per hour per degree dif- 
ference in temperature will be 

Volume of air X air changes per hour 
55 

As it is usually impractical to estimate the amount of air 
displaced by partitions, floors, interior furnishings, etc., the 
term "volume of air" in the above expression is taken as the 
total gross volume of the building less 10 per cent. The above 
expression then becomes 

90 per cent, of the gross volume X air changes per hour 

55 ~~ 

or 

gross volume X air changes per hour 
60 

The next step consists of selecting the heat transmission 
factors for glass and the materials of which building walls are 
usually composed. The loss of heat through a square foot of 
ordinary window glass per hour per degree difference in temper- 
ature is taken as 1 B. T. U., and the corresponding losses through 
brick and granite walls of the usual thicknesses are taken as 
.2 and .3 B. T. U. respectively. By thus providing for the 
loss of heat due to transmission, an expression is obtained for 
the total heat units lost per hour per degree difference in tem- 
perature. This expression is 

Gross vol. X Air charges per hour _, . . „ , 

— ™ — - — +Square feet of glass + .2X 

square feet of wall. 

Instead of next proceeding to make an assumption as to the 
average difference in temperature between the outside and the 
inside air, which, together with an assumed number of hours 
during which heating occurs, would result in an expression for 
the total heat loss in B. T. U. during the heating season, the 
expression in the above form was applied to what was considered 
to be an average building that was satisfactorily heated and 
had neither too much nor too little radiating surface installed. 



12 ENGINEERING FOR CENTRAL STATIONS 

This resulted in a factor which is considered as being constant 
for any given locality, the value for Boston being 5.4. This 
factor represents numerically the number of B. T. U. lost per 
hour per degree difference in temperature between the outside 
and the inside air for each square foot of radiating surface. 
Consequently, when the expression given above is divided by 
this factor, the quotient will represent the proper amount of 
radiating surface in square feet for any given building. This 
radiating surface is then divided by 130, which is considered to 
be the average amount of radiation that can be supplied by one 
boiler horse-power throughout the heating season under the 
conditions existing in Boston, and the quotient thus obtained 
represents the average boiler horse-power required during the 
heating season. The final equation, in its general form, is as 
follows : 



V ~ + C 1 XG+C 2 XW 

Tons of coal per year = — =« xLxdXhX 

C 3 X (loU J. ) 

34.5 

eX2000 



In the above equation 

V = gross volume of the building, including basement if 

heated. 
G = square feet of glass surface, 10 per cent, being added for 

north and west exposures. 
W = square feet of wall surface, 10 per cent, being added for 

north and west exposures. 
a = average air changes per hour during heating period. 
C t = constant for glass = 1 for single glass. 
C 2 = constant for wall, usually .2 for brick and .3 for stone. 
C 3 = constant for local conditions = 5.4 for Boston. 
T = factor dependent upon the relation the heating plant bears 

to the premises heated. 
L = factor for portion of building not heated, or for building 

not heated to 70° F. 
e = average evaporation in pounds of steam per pound of coal. 
d = number of heating days during season. 
h = average number of hours of heating per day. 



AMOUNT OF COAL REQUIRED 13 

The values of h for different classes of buildings are given as 
follows: 

Hotels, 15 to 16 hours. 
Apartment houses, 12 to 14 hours. 
Department Stores, 10 to 12 hours. 
Office buildings, 10 to 12 hours. 
Theaters, 6 to 10 hours. 

It will probably be conceded that this formula is altogether 
too complicated for ordinary practical use. As previously 
mentioned, its accuracy, in any particular case, depends upon 
the value assigned to each of the several variables. A slight 
error in each of these assigned values might, by a cumulative 
action, lead to a total error of considerable magnitude. More- 
over, the method employed in obtaining the so-called constant 
C 3 ( = o.4 for Boston) introduces a considerable element of uncer- 
tainty, inasmuch as it would, conceivably, be an extremely 
difficult matter to detremine absolutely whether a certain build- 
ing had exactly the proper amount of radiating surface for its 
heating requirements. 

While there are a number of other methods employed for 
estimating the heating requirements of a given building, they 
are all, of necessity, based upon the same general principles as 
those which have determined the methods outlined above, and 
they therefore differ from the methods described only in the 
manner in which they deal with the various constants and 
variables of which any heating formula is necessarily composed. 



CHAPTER II 

COOLING THE AIR OF BUILDINGS BY MEANS OF 
MECHANICAL REFRIGERATION 1 

One frequently hears expressions of surprise over the fact 
that the artificial cooling of the air in our dwellings, our public 
buildings and our places of amusement is not more general. In 
other words, why is it that, in our modern social and industrial 
life, we have not felt the necessity of maintaining our homes 
and our places of business and of pleasure at a temperature as 
conducive to comfort during the heat of the summer as during 
the cold of the winter? To the lay mind, observant of the mani- 
fold comforts of which mankind is now the beneficiary and 
which have largely resulted from the rapid mechanical and 
electrical developments of the past few years, the question is 
quite a natural one. 

To begin with, the period during which artificial cooling is 
required — at least throughout the temperate zone — is very 
much less than the time during which artificial heating is a 
necessity. If we assume that 70° F. is the temperature which 
is most pleasing to the vast majority of persons — admitting the 
fact that one occasionally encounters an individual who evinces 
a preference for a temperature of 60° F. or thereabouts — we will 
note, from a glance at Fig. 3, how small that portion of the entire 
year is in which the average outside temperature is in excess of 
70° F., and, by comparison, how large the portion is during 
which the outside temperature is below 70° F. The stepped 
curves in Fig. 3 show the mean monthly temperatures through- 
out the year of New York City, Chicago, Portland, Me., and 
New Orleans, respectively, the temperatures as given being 
averages for a long period of years. It will be seen that in no 
month during the year does the mean temperature of Portland, 
Me., reach 70° F., while in New York City and Chicago a higher 
mean temperature than 70° F. exists only during some 2 
months of the entire year. Even in the case of New Orleans, 
only 5 months out of the entire year show a mean monthly 
temperature in excess of 70° F. 

1 This Chapter first appeared as an article in Power, Vol 34, p. 820. 

14 



COOLING THE AIR OF BUILDINGS 



15 



Supplementing the less urgent need of artificial cooling, due 
to the very restricted period during which it is ordinarily required, 
is the fact that its production is attended with much greater 
complication and with decidedly more expense than is the pro- 
duction of artificial heat. The cooling of air, as will be explained 
further on, is not, as a general rule, simply a reversal of air 
heating, but it usually involves the removal of moisture from 
the air, and this has a very material bearing upon the question. 



o c 

a « 

a to 

o <u 











































































80° 










































































70° 
60° 
50° 














I — 


















N 


ew 


rC 


rlea 


as 






— 








=* 






- 




























































































































































70° 






































































— 




60 3 


































Po 


rt 


ar 


d, 


M 






























50" 




















































































40 J 
30° 
















































































70° 










































































60° 






































































50° 


































C 


11C 


ag 


'O 










































































































40° 
















































































30" 
















































































70° 
60° 
















































































































































































N 


ew 


Y 


or 


kCi 


ty 






























50 u 
40° 
30° 

































































































































































































































Jan. Feb. Mar. Apr. May June July Aug. Sept. Oct. Nov. Dec. 

Fig. 3. — Showing mean monthly temperatures in four cities of the 

United States. 



In addition to all mechanical and financial considerations is 
the one of hygiene, which, naturally, is of paramount importance. 
In passing from an outside temperature of 0° F. into a room 
heated to 70° F. one experiences no unpleasant consequences, 
but a reversal of the procedure, without the acquisition of any 
additional clothing, is liable to have serious results. Even 
passing from an outside temperature of 90° F. or so into a room 
held at 70° F., might, particularly if a person were extremely 
warm when entering the room of lower temperature, have serious 
consequences as a result of the sudden chilling of the surface of 
the body, and the consequent disturbance of the bodily func- 
tions. It would appear, therefore, that, should the artificial 
cooling of buildings become at all common, considerable care 



16 ENGINEERING FOR CENTRAL STATIONS 

must be exercised by those entering such buildings from a con- 
siderably higher outside temperature, if " colds" or more serious 
forms of bodily disorders are to be avoided. It does not appear, 
however, that this will place any very serious difficulty in the 
way of a considerably more extended use of mechanical refrigera- 
tion for the purpose of artificially cooling the air of buildings, 
and it is reasonable to believe that the future will witness a con- 
siderable development along these lines. 

Air cooling has already assumed considerable commercial 
importance in several industries, notably in the manufacture 
of chocolate and in the operation of blast furnaces. Before 
chocolate manufacturing plants were artificially cooled, it was 
difficult, if not impossible, to continue the operation of such 
plants during the extremely warm periods of the year. In the 
case of blast furnaces, the cooling of the air is done for the pur- 
pose of removing its moisture, thereby making it possible to 
reduce to some extent the amount of coke used, inasmuch as 
when moisture is present in the air, a portion of the total fuel is 
used in heating this moisture. 

Coming to the physical considerations involved in the cooling 
of air we are confronted with the fact that air is, in reality, 
a mixture of air and vapor. When air is warmed, this moisture 
is heated along with the air, but its weight is so small compared 
with that of the air that the presence of this moisture, so far 
as having any effect upon the quantity of heat required, can 
usually be ignored. When air is cooled, however, the moisture 
in the air must be removed step by step, provided a condition 
of saturation is reached — a condition to be met with in a practical 
case of air cooling. The removal of this moisture in the air 
necessitates the abstraction of an amount of heat, for every 
p und of vapor present, equivalent to the heat of vaporization 
of water, which is, roughly, 1000 B. T. U. per pound. In 
addition to this, a quantity of heat must be removed from the 
air itself, and this quantity is represented by the product of 
the number of pounds of dry air present, the specific heat of 
air, which is usually taken at .238, and the range of temperature 
through which the air is cooled. A small additional quantity 
of heat must be removed in order to cool the varying amount of 
vapor present from its initial to its final temperature. This 
quantity is relatively so small — probably averaging 2 or 3 per 
cent, of the total heat abstracted in cooling the air and removing 



COOLING THE AIR OF BUILDINGS 17 

the moisture — that it can practically be neglected, although an 
additional allowance of some 2 or 3 per cent, is frequently made 
to cover this item. 

In order to determine the capacity of the refrigerating ma- 
chinery necessary to maintain a given room or building at a 
predetermined temperature and relative humidity, under 
certain prescribed conditions of outside temperature and 
humidity, the engineer must not only be able to predict with con- 
siderable accuracy the amount of heat that will enter the room 
or building in question from the outside, under the conditions 
assumed, but he must also make proper allowance for the 
amount of heat generated within the room or building, both by 
its human occupants and the illuminants which are used. The 
determination of this total gain of heat, however, does not fully 
solve the problem. 

The method of air cooling now usualty employed is practically 
the same in principle as the indirect system of heating. Air is 
forced by a fan through refrigerating coils, and frequently water 
is sprayed over these coils as the air is passing through them, the 
water thus serving to wash the air and, at the same time, to 
cool it. When ammonia is used as the refrigerating agent, it is 
usual to circulate refrigerated brine through the coils, but when 
carbonic acid is the refrigerating medium, direct expansion 
usually takes place within these coils, thus dispensing with the 
use of refrigerated brine. From the cooling chamber the air is 
led through ducts to the room or rooms to be cooled. The 
quantity of air which is thus circulated in a given time between 
given temperature limits and from a given initial relative 
humidity, determines the capacity of the refrigerating machine. 

It is evident that the temperature of the air as it leaves a 
room or building, with such a system as that just outlined, 
will be slightly above the average temperature within such 
room or building after uniform conditions have been reached. 
The gain in temperature which a given weight of air experiences 
in its passage through a room or building is a measure of the 
heat which it removes, and this must be equivalent to the 
quantity of heat which gains access to, and which is generated 
within, the room or building in order that the inside tempera- 
ture may remain constant. It is evident, therefore, that the 
removal of the heat may be effected either by moving a com- 
paratively small weight of air through a considerable range of 

2 



18 ENGINEERING FOR CENTRAL STATIONS 

temperature, or by moving a larger weight of air between 
narrower limits of temperature. The former is more conducive 
to refrigerating economy, for while the refrigerating require- 
ments per pound of air are somewhat greater, the number of 
pounds of air handled are enough less to more than offset this 
difference, the saving being due to the smaller amount of 
moisture which must be removed by condensation. 

While it is thus desirable, from a refrigerating point of view, 
to keep the weight of air that is circulated at a minimum, 
practical considerations usually fix the lower temperature limit 
to which the air may be cooled, this limit naturally being depend- 
ent upon the temperature of the cooling coils, upon their depth 
in the direction of the air flow and upon the velocity with which 
the air passes through the coils. The question of supplying an 
amount of air sufficient for proper ventilation and for adequate 
diffusion is also a limitation which must be observed. On the 
other hand, a small temperature range with large volume of air 
finds a limitation in the danger of producing annoying air 
currents which, being of low temperature, are liable to become 
a menace to health. The question of final relative humidity is 
also one which has a bearing upon the temperature to which the 
air must be cooled, inasmuch as the air should always leave the 
cooling coils in a saturated condition, thereby making its final 
relative humidity dependent upon the range in temperature 
through which the air is allowed to warm. 

Mention has been made in a preceding paragraph of the heat 
generated within the building by its human occupants and by 
the illuminants which are used. It is stated by authorities that 
the average adult individual will emit about 400 B. T. U. per 
hour while at rest, and that this emission is practically doubled 
when the individual is engaged in physical work. Hence, when 
a considerable number of people are congregated within doors, 
the quantity of heat which they generate may b considerably 
in excess of that which enters as a result of the difference between 
the outside and inside temperatures. An average adult person 
will, moreover, give off, by exhalation and evaporation, an 
amount of moisture ranging from 1/16 to 1/4 of a pound per, 
hour, according to circumstances. This amount of moisture is 
usually so small, however, compared with the amount which is 
carried by the refrigerated air, that it does not affect materially 
the question of final relative humidity. 



COOLING THE AIR OF BUILDINGS 



19 



To give some idea of the amount of heat produced by a few 
of the more common types of illuminants, the following table is 
presented, based upon data compiled by various authorities: 



Type of illuminant 


Quantity consumed 
per hour 


Candle-power 
of illuminant 


Heat produced 

per hour in 

B. T. U. 

(approx.) 


Grains 


Cu. ft. 




2,200 
909 




16 


5,600 
4,100 
4,100 
3,000 
1,800 
2,000 
170 

SO 








5.5 
3.5 


16 

50 

400 


















16 
20 


descent lamp. 
25-watt tungsten filament in- 
candescent lamp. 











While the values given in the above table are only approxi- 
mate, the superiority of the electric light as a non-heat-producing 
form of illuminant is very clearly shown. Moreover the incan- 
descent electric lamp possesses the material advantage of not 
consuming the oxygen of the air and of not vitiating the air 
with any products of combustion. 

In order to show the application of some of the principles 
which have been enumerated above, a practical case of air 
cooling, to meet certain specified conditions, will be worked out 
in detail. We will assume, for convenience, a large room, 100 
ft. square and with a 30-ft. ceiling and exposed to the outside 
air on all four sides. If the specifications stipulate that the 
temperature of this room shall not exceed 75° F. when the 
outside temperature is at 90° F., it might readily work out that 
the total amount of heat entering this room through the side 
wals, windows, floor and ceiling would amount to some 200,000 
B. T. U. per hour. The following additional assumptions will 
be made: that the room is to accommodate a maximum of 
500 people; that it is to be lighted by 300 twenty-five watt tungsten 
lamps, and that the relative humidity within the room is not 
to exceed 60 per cent, when the relative humidity of the outside 
air is 80 per cent, for the limits of temperature as given above. 

Upon the assumption that the persons who are to occupy this 
room are to be at rest, we will take a heat emission of 400 B. T. U. 
per person per hour, which, for a maximum of 500 people, would 



20 ENGINEERING FOR CENTRAL STATIONS 

amount to 200,000 B. T. U. per hour. Referring to the foregoing 
table showing the heat given off by various types of illuminants, 
we will take the value of 80 B. T. U. as the amount of heat 
given off per hour by a 25-watt tungsten lamp. The total 
amount of heat emitted per hour with the entire lighting instal- 
lation in use would, therefore, amount to 24,000 B. T. U. It 
thus appears that our refrigerating plant must be capable of 
removing from the room under consideration a total of approxi- 
mately 424,000 B. T. U. per hour. 

The next step is to select the range of temperature through 
which the air shall be allowed to warm while passing through the 
room. As remarked above, it is desirable from a refrigerating 
point of view that this temperature range be as great as possible, 
and thereby reduce the total quantity of air that must be circu- 
lated, but, as previously noted, there are certain practical limi- 
tations to such a procedure. We will start by assuming a 
temperature rise within the room of 15°, the air entering at 60° 
and leaving at 75° F. As there will be an unavoidable rise in 
temperature between the cooling coils and the points where the 
cool air enters the room, we will assume that the air will leave 
the cooling coils at a temperature of 55° F. Taking the specific 
heat of air as .238, it will be found that approximately 120,000 
lb. of air must be supplied per hour to remove the total amount 
of heat that has been determined above, with a temperature 
rise of 15° within the room. This would be equivalent to over 
five changes of air per hour and would afford excellent ventilation 
for the maximum number of people that has been assumed. 

If we calculate the amount of moisture that is present for 
each pound of dry air, for the assumed outside temperature of 
90° F. and 80 per cent, humidity, as may easily be done by 
consulting a table showing the properties of saturated air at 
various temperatures, and if we then make a similar calculation 
to determine the amount of moisture that is present with each 
pound of dry air at a temperature of 55° F., which is the tempera- 
ture at which the air is assumed to leave the refrigerating coils 
in a saturated condition, we shall find that approximately 15.5 
lb. of moisture must be condensed for each 1000 lb. of dry air 
supplied. As we have already found the required quantity of 
dry air to be 120,000 lb. per hour, it is evident that about 1860 
lb. of moisture must be condensed per hour, requiring an abstrac- 
ts of heat amounting, roughly, to 1,900,000 B. T. U. per hour. 



COOLING THE AIR OF BUILDINGS 21 

We must now allow for the rise in the temperature of the air 
during its passage from the refrigerating coils to the room 
outlets. As we have assumed a 5° rise in the temperature of 
the air while passing through the ducts, the total gain of heat 
from this source will be 5 X. 238 X 120,000, or approximately 
143,000 B. T. U. The total amount of heat that our refrigerating 
plant must be capable of removing per hour is, therefore, as 
follows: 

B. T. U. 
Heat radiated through walls, windows, floor and ceiling. 200,000 

Heat emitted by human occupants 200,000 

Heat resulting from illuminants 24,000 

Heat of liquefaction of vapor removed by condensation. 1,900,000 
Heat gained in passage through ducts after leaving 

refrigerating coils 143,000 

Heat between 90° and 75° F 428,400 

Total 2,895,400 

The capacity of a refrigerating machine is expressed in tons 
of refrigeration, a ton of refrigeration being equivalent, in cold- 
producing effect, to the melting of one ton of ice in 24 hours. 
One pound of ice, in changing into water at the same temperature 
(32° F.), absorbs from its surroundings approximately 142 B. T. 
U. ; therefore, the melting of one ton of ice is accompanied by 
an absorption of heat amounting to 284,000 B. T. U. The 
"ton of refrigeration/ ' or "ton of refrigerating effect/' is, there- 
fore, equivalent to the removal of 284,000 B. T. U. in 24 hours, 
or of 12,000 B. T. U., roughly, in 1 hour. Hence, by dividing 
the total number of B. T. U. that our refrigerating plant must 
remove per hour, as given above, by 12,000, we find that it 
should have a capacity of approximately 240 tons of refrigeration. 
Allowing an additional 2 1/2 per cent, for the cooling of the 
varying amount of vapor that is present with the air, the 
required refrigerating capacity would be about 246 tons. 

One of the conditions assumed in the foregoing problem was 
that the final relative humidity within the room should not 
exceed 60 per cent. As stated previously, for any given temper- 
ature to which air is cooled, the final relative humidity will 
depend upon the range of temperature through which the air is 
afterward allowed to warm, assuming the air to be in a saturated 
condition when it leaves the cooling coils — a condition always to 
be met with in problems of air cooling. This is due to the fact 



22 



ENGINEERING FOR CENTRAL STATIONS 



that a given weight of air, when leaving the cooling coils, carries 
with it a definite weight of moisture, and this weight remains 
constant, inasmuch as the air passes over no water and hence 
has no opportunity for gaining any additional moisture. Satu- 

DlRECTIONS FOR USING CHART 

Intersect diagonal line corresponding to initial temperature by horizontal 
line corresponding to final temperature; from point of intersection drop a 
line to the scale to find the number of tons for cooling the air. Find the 
diagonal line correspond- 
ing to the weight of vapor 
present in the incoming 
air supply; intersect this 
diagonal by a vertical line 
corresponding to the weight 
of vapor present in the sat- 
urated air at final temper- 
ature; from the point of 
intersection run a line hori- 
zontally to the scale to 
find the number of tons for 
condensing the vapor. 




1 

5 4 3 2 1 

Tons of Refrigerating Capacity for 
Cooling Air per 1000 Cu. Ft. per Min. 

Fig. 4. — Chart for determining approximately the amount of refrigeration 
required for a given case of air cooling. 

rated air at 55° F., if warmed to 75° F., will have a final relative 
humidity of approximately 50 per cent. This is sufficiently 
below the limit that was specified in our problem to provide 
for the unavoidable increase in moisture that would result from 
the people present in the room. 



COOLING THE AIR OF BUILDINGS 23 

The accompanying chart, Fig. 4, is reproduced from a paper 
upon the subject of air cooling that was read by W. W. Macon 
before t e American Society of Heating and Ventilating Engi- 
neers. It affords a very convenient method of determining the 
approximate refrigerating capacity required for a given case of 
air cooling after the necessary preliminary calculations have been 
made to determine the requisite volume of air that is to be sup- 
plied. The chart shown herewith was derived from another chart 
showing the B. T. U. that must be removed per pound of dry 
air for cooling the air and for condensing the accompanying vapor, 
the heat units per pound of dry air being converted into tons of 
refrigeration per 1000 cu. ft. of air by assuming an average alue 
of .07 lb. as the weight of dry air in a cubic foot of a mixture of 
air and vapor. The variation from this value is not great for 
the range of temperatures and percentages of humidity found 
in an ordinary case of air cooling, the actual weights ranging 
from .0659 for air at 102° F. and 100 per cent, humidity, to 
.0737 lb. for air at 72° F. and 50 per cent, humidity. 

To show the method of applying this chart, we will employ it 
for determining the refrigerating capacity under the conditions 
of the problem worked out in detail above. We found that 
approximately 424,000 B. T. U. must be removed from the 
room each hour, with the air entering the room at 60° and leaving 
it at 75° F., a rise of 15°. One cubic foot of a mixture of air and 
vapor at a temperature of 60° F. with a relative humidity of 
approximately 85 per cent., when heated through 15° will take 
up 1X15X.075X.238 = .268 B. T. U. The removal of 424,000 
B. T. U. per hour is equivalent to removing 7066 B. T. U. per 
minute. Dividing this latter quantity by .268, we obtain 26,366 
cu. ft. per minute as the quantity of air entering the room. 
Xow referring to the chart and following out the course of the 
dotted lines, we find that approximately 2.92 tons of refrig- 
eration are required for cooling the air, and 5.66 tons for con- 
densing the vapor, for each 1000 cu. ft. of air supplied per 
minute. The required refrigerating capacity is, therefore, 
2.92 + 5.66 = 8.58 multiplied by 26.36, which amounts to 226 
tons. Increasing this amount by 2 1/2 per cent., gives a 
capacity slightly in excess of 230 tons, which is somewhat 
below the figure previously obtained. This is due to the fact 
that in the chart the weight of the dry air in a cubic foot of a 
mixture of air and moisture is taken as .07 lb., whereas the actua 



24 ENGINEERING FOR CENTRAL STATIONS 

weight of this air, under the conditions of our problem, is .075 lb. 
This is equivalent to a difference of 7 per cent, which is, approxi- 
mately, the percentage difference in the refrigerating capacities 
as determined by the two methods. 

Certain features of interest in connection with a few of the 
more important air cooling installations now in use in this 
country will be briefly mentioned. One of the most notable 
is probably that of the New York Stock Exchange, which, at 
the time of its installation, was probably the largest air-cooling 
problem that had ever been undertaken. The refrigerating plant 
comprises three units of the absorption type of 150 tons capacity 
each. The refrigerating capacity provided is such that a temper- 
ature of not over 75° F. and a relative humidity not to exceed 
55 per cent., shall be maintained when the temperature of the 
outside air is 85° F. and the relative humidity 85 per cent. 

The Auditorium Hotel in Chicago is equipped with an air- 
cooling system of considerable magnitude. The total space 
cooled is stated as being approximately 500,000 cu. ft. and 
comprises the banquet hall, reception rooms, etc. An average 
difference of some 14° is maintained between the temperature 
in these rooms and that of the office and main corridor during 
the summer season; while a difference of some 20° is usually 
maintained during hot weather between the temperature within 
these rooms and the temperature of the outside air. The C0 2 
system is employed — expansion of the gas occurring within the 
cooling coils. The C0 2 compressor is driven by an electric 
motor. It has been stated that the cost of operating this 
system is approximately $20 per day, which includes the cost 
of power, water and labor but is exclusive of interest and 
depreciation. 

The new Blackstone Hotel in Chicago has an extensive air- 
cooling system which takes in the main restaurant, banquet hall, 
cafe, grill room and barber shop. Carbonic acid gas is employed 
here also as the refrigerating agent, the gas expanding directly 
into the cooling coils. Water is sprayed over these coils by 
means of a small centrifugal pump, the water being cooled to 
about 45° or 50° F. in passing over the coils, while the gas within 
the coils is usually expanded at a temperature of about 20° F. 
The outside air, in being drawn through this cold spray and 
through the cooling coils experiences a drop in temperature of 
some 16° or 20°, and leaves the cooling chamber in a saturated 



COOLING THE AIR OF BUILDINGS 25 

condition, thoroughly washed and at a temperature ranging 
from about 60° to 65° F. Three separate cooling chambers 
have been provided, each having its own blower and connections, 
by means of ducts, with the room or rooms which it serves to 
cool. The blowers are of the double-intake type and maintain 
a pressure of from 3/4 to 1 oz. The ducts are made of sheet 
metal and are provided with 1-in. asbestos air-cell covering. 
The air enters the room through ornamental registers located 
at a distance of some 8 ft. from the floor; while the exhaust is 
taken from both the floor and the ceiling in order to promote the 
circulation of the air. Rheostats automatically regulate both 
the supply and the exhaust. It is claimed that, within the 
rooms which are equipped with this system, the average tem- 
perature during extremely warm weather is maintained at 
least 20° below the temperature of the outside air. 



CHAPTER III 

MECHANICAL REFRIGERATION FOR THE COLD STORAGE 1 
OF FURS AND FABRICS 

The placing of furs and such fabrics as carpets ; tapestries, 
clothing, woolens, etc., in cold storage in order to protect them 
against the inroads of those insects which prey upon them during 
certain portions of the year, is now generally recognized as the 
most satisfactory method of dealing with this important prob- 
lem. The annual loss arising from the destruction of those 
classes of merchandise which have been mentioned by the rav- 
ages of the moth and the beetle cannot be even approximately 
estimated, but the yearly toll which is thus exacted is unques- 
tionably tremendous in the aggregate, and any means of reduc- 
ing this loss is therefore worthy of serious consideration from 
an economic point of view. 

The first storage warehouse in this country to undertake the 
cold-storage of furs, carpets and other fabrics, was apparently 
that of the American Security & Trust Company of Washington, 
D. C, which provided cold storage facilities for these classes of 
goods in the year 1894. For two years thereafter, the manager 
of the cold-storage department of this company, Mr. Albert M. 
Read, with the assistance of Dr. L. O. Howard, Chief of the 
Bureau of Entomology of the United States Department of 
Agriculture, carried on a series of extremely interesting and 
valuable tests for the purpose of determining the effects of 
various temperatures upon the larvae of the moth and beetle. 
These were probably the first tests which had ever been con- 
ducted along similar lines, and the results which were secured 
served largely as a basis for the subsequent commercial develop- 
ment which has occurred in the use of cold storage for the pro- 
tection of furs and fabrics. 

The cold storage of furs at first encountered the opposition of 
many of the furriers, who had previously derived a considerable 
portion of their income from the care of their customers' furs 
during the summer months, such care usually involving a fre- 
quent brushing and shaking of the furs, separated by intervals 

J This chapter first appeared as an article in Power, Vol. 35, p. 261. 

26 



; REFRIGERATION OF FURS AND FABRICS 27 

during which they were packed away with camphor, tar paper, 
or some other similar moth-repelling substance. However, 
such opposition gradually disappeared and to-day the leading 
furriers either operate their own cold-storage vaults or else rent 
storage space in cold storage warehouses. The latter are rarely 
so located that they may be conveniently reached by the class 
of patrons which a furrier serves, and this doubtless accounts 
for the fact that the majority of the furriers and department 
stores usually maintain their own refrigerated rooms for the 
storage of furs. 

In the experiments referred to above it was found that any 
temperature below 45° F. was sufficient to keep the larvae of 
both the moth and beetle from doing any damage to furs or 
fabrics, although the larvae were capable of sluggish movement 
at a temperature as low as 42° F. Below 40° all movement was 
suspended and the larvae become entirely dormant, Avhile above 
45° activity of the larvae began and increased with each degree 
of increase in temperature up to 55° when a normal condition as 
regards activity was reached. It was found that the larval 
condition of the insects in question was the one in which the 
damage to the furs and fabrics occurred, inasmuch as the grease 
and animal juices in the fiber of the fur and wool serve as food 
for the larvae of both the moth and the beetle while these insects 
are passing through this stage of their existence. It was found 
that the larvae of both of these insects could withstand a tem- 
perature as low as 18° F. for a long period without harmful effects 
and that they changed back from a dormant to an active con- 
dition when the temperature again became normal. However, 
if repeatedly exposed to considerable changes in temperature, 
the vitality of the larvae of these insects was found to be consider- 
ably reduced — a fact which should cause a winter composed of 
alternating periods of cold and mild weather to be followed by a 
summer of decreased insect life. It was found that the miller 
and beetle were soon killed when subjected to temperatures 
below 32° F. and that they gradually died if exposed to tem- 
peratures between 32 and 40° F. 

While these investigations showed that cold storage rooms for 
the preservation of furs and fabrics may be kept at 40° F. with 
perfect safety, the temperatures most commonly carried in cold 
storage rooms to-day range from 20 to 26° F. At these lower 
temperatures the furs retain a fresh and glossy appearance, and 



28 ENGINEERING FOR CENTRAL STATIONS 

the flexibility of the skins is preserved as a result of a lessening of 
the evaporation of the natural oils which they contain. 

Two different methods of applying mechanical refrigeration 
to the cold storage of furs and fabrics are in general use at the 
present time. One of these is known as the direct system and 
the other as the indirect. Each system possesses certain advan- 
tages as well as certain disadvantages. In the direct system the 
refrigerating coils — either arranged for direct expansion or for 
the circulation of brine — are placed within the storage room 
itself, being mounted upon the side walls or ceiling, or upon 
both. The indirect system comprises an air-cooling room or 
bunker space in which the refrigerating coils are located, this 
space being entirely separate from the room which is to be 
refrigerated, but connected with it by a system of ducts through 
which the refrigerated air is circulated by means of a fan. The 
advantages of the direct system, as compared with the indirect, 
are that it is somewhat cheaper to install and also to operate: 
the first, because of the elimination of the air-cooling chamber 
and air-circulating fan, although this is partially offset by the 
somewhat greater cost of the piping for the cooling coils; the 
second, because it is unnecessary to operate an air-circulating 
fan, which requires the expenditure of an appreciable amount of 
energy. With either system the employment of brine as the 
cooling medium adds materially to the first cost of the instal- 
lation, and likewise increases the cost of operation due to the 
necessity of constantly circulating the brine. The use of brine 
arises from the fear of a leak in the ammonia piping, with a con- 
sequent damage fo the goods in storage. Where the ammonia 
piping is carefully installed and well tested before being placed 
in operation, danger from the leakage of ammonia gas is probably 
not great, as the successful operation of the large number of 
plants which are employing ammonia as the refrigerating agent, 
bears witness. However, in view of the very heavy financial 
responsibility that is usually involved where furs in any quantity 
are held in storage, this question is undoubtedly one of consider- 
able importance, and where ammonia is employed as the refrig- 
erating agent, the indirect system, with brine as the secondary 
cooling medium, undoubtedly offers the greatest amount of 
security against any damage to the articles in storage from the 
refrigerating medium itself. The indirect system has the further 
advantage of freeing the storage space of the moisture which 



REFRIGERATION OF FURS AND FABRICS 29 

collects as frost on the piping and which melts and drips from the 
pipes if the temperature rises above the freezing point. The air 
in the storage space is therefore drier where the indirect system 
is used, and this is an advantage, provided the percentage of 
moisture is not reduced too far, a condition which can easily be 
prevented. 

One of the arguments advanced against the indirect system is 
that it involves an increased fire risk, inasmuch as the movement 
of the air in the storage space might tend to fan a fire if one 
should happen to occur. The belief in such a possibility was 
doubtless considerably strengthened by a fire, involving a very 
heavy financial loss, which occurred in the fur cold-storage room 
of a large department store in Brooklyn a few years ago. The 
origin of this fire has been somewhat of a mystery, but it has been 
generally contended that the system of air circulation that was 
in use was in some way responsible for the serious nature of 
the fire. As a result of this fire, the New York Fire Insurance 
Exchange made certain recommendations as to the manner in 
which the indirect system of refrigeration for fur storage rooms 
should be installed. These recommendations call for the air 
duct or ducts to be equipped with automatic dampers, arranged 
to be controlled by fusible links properly installed; the blower or 
fan to be equipped with an automatic "stop" or "controller," 
arranged to be operated either by electric thermostats having a 
low fusing point, or thermometers having proper attachments 
installed within the cold-storage room, and that these devices 
be adjusted to operate the "stop" or "controller" on the blower 
or fan so that when the temperature rises to 100° F. the blower 
or fan will shut down. When these recommendations are 
observed, it would not appear that this system offers any 
material increase in fire risk over the direct system of 
refrigeration. 

The refrigerating requirements for given outside temperature 
conditions, and for a given maintained temperature within the 
cold-storage space, are, of course, directly dependent upon the 
insulation that is provided for the floor, walls and ceiling of the 
room which is to be refrigerated. As the insulation that is 
provided in different installations varies greatly in its effective- 
ness in limiting the passage of heat from the outside to the 
inside of the refrigerated space, if is of course impossible to 
estimate, even approximately, the refrigerating requirements for 



30 ENGINEERING FOR CENTRAL STATIONS 

a given volume of cold-storage space without a knowledge of 
the character of the insulation that is to be employed. This is 
particularly evident when we consider that with some of the 
different combinations of insulating materials that are in ordi- 
nary commercial use we may obtain variations in heat trans- 
mission varying from less than 1 to nearly 5 B. T. U. per 24 
hours per square foot of exposed surface for each degree of 
difference between the inside and outside temperatures. Table 
III shows the approximate number of B. T. U. that are trans- 
mitted per square foot per 24 hours for each degree of tempera- 
ture difference for several different types of insulation that are 
commonly met with in practice. 

The number of cubic feet of refrigerated space per ton of refrig- 
eration naturally varies with the size of the space refrigerated t 
other conditions remaining the same, inasmuch as the exposed 
surface through which the gain of heat occurs does not increase in 
proportion to the increase in the volume of the refrigerated space. 
It is also affected somewhat by the system of refrigeration that 
is employed — that is, whether the direct or the indirect system 
and whether or not brine is used as a secondary cooling medium. 
As in all other problems of refrigeration, the question of insu- 
lation is of paramount importance, and the saving in the cost 
of power required for refrigeration will almost invariably pay a 
large return upon the money invested in a high grade of insulation. 

Table IV shows the capacity of the refrigerating plant installed, 
the cubical contents of the space refrigerated, the volume of 
refrigerated space and the total exposed surface per ton of 
refrigerating plant capacity, together with the system of refrigera- 
tion that is employed, for a number of electrically driven 
refrigerating plants which are used in connection with the cold 
storage of furs and fabrics. 

Table V gives some consumption figures for motor-driven 
refrigerating plants used exclusively for the cold storage of furs. 
In cases 2 and 4, the compressor motors were not separately 
metered during the month of May, so the consumption figures 
cover a period of 11 months only. In cases 1 and 3, the con- 
sumption figures cover an entire year, athough these plants 
were in actual operation only during some seven or eight months 
of the year. 

It is somewhat surprising to observe how low the load factor 
is in these plants, even during the months of mid-summer. 



REFRIGERATION OF FURS AND FABRICS 



31 



Based on the rating of the motor which drives the compressor, 
plant 1 operated at rated load for only 10 per cent, of the time 
during July, which was the month of greatest consumption; 
while for the entire period (May to October, inclusive) this 

TABLE III 



Character of insulation 



B. T. U. per square 
foot per 24 hours per 
degree difference he- 
tween outside and 
inside temperatures 



Double 7/8-in. boards and paper, 1-in. air space, 5-in. sheet cork 

paper and 7/8-in. board. 
Double 7/8-in. boards and paper, 1-in. air space, 4-in. sheet cork, 

paper and 7/8-in. board. 
Two 7/8-in. boards and paper, 8-in. mill shavings, two 7/8-in. 

boards and paper. 

Same slightly moist 

Same damp 

Double 7/8-in. boards and paper, 4-in. granulated cork, double 7/8- 
in. boards and paper. 
One 7/8-in. board and paper, 3-in. sheet cork, paper, one 7/8-in. 

board and paper. 
One 7/8-in. board, 6-in. patent silicated strawboard (air cell), 

finished with thin layer patent cement. 
Four double 7/8-in. boards with paper between (eight boards in all) 

and three 8-in. air spaces. 
One 7/8-in. board, paper, 2-in. sheet cork, two 7/8-in. boards and 

paper. 
Two 7/8-in. board and paper, 1-in. sheet cork, two 7/8-in. boards 

and paper. 
Two 7/8-in. double boards and two papers, 1-in. hair felt between. . 
One 7/8-in. board and paper, 2 1/2-in. mineral wool, paper and 

7/8-in. board. 
Two 7/8-in. boards and paper, 1-in. air space, two 7/8-in. boards 

and paper. 

One 7/8-in. board, 2-in. pitch, one 7/8-in. board 

One 7/8-in. board, 1-in. pitch, one 7/8-in. board 



1.20 

1.35 

1.80 
2.10 

1.70 

2.10 

2.48 

2.70 

3.00 

3.30 

3.32 
3.62 

3.71 

4.25 
4.90 









TABLE 


IV 












Square feet 




Capacity 


H. P. of 


Cubical 


Cubic feet 


of surface 




of plant 


motor 


contents 


of storage 


(floor, ceil- 




tons of 


driving 


of storage 


space per 


ing and side 


System 


refrigera- 


refriger- 


space in 


ton of re- 


walls) per 




tion 


ating 
plant 


cu. ft. 


frigeration 


ton of re- 
frigeration 




50 




155,000 
60,000 


3,100 
3,000 






20 


35 


748 


Indirect — ammonia coils 


15 


25 


40,500 


2,700 


651 


Indirect — ammonia coils 


10 


15 


32,700 


3,270 


805 


Direct — ammonia coils 


4 


7 1/2 


5,720 


1,430 


569 


Direct — ammonia coils 



32 ENGINEERING FOR CENTRAL STATIONS 

TABLE V 





1 
Four- ton com- 
pressor belt- 
driven by 1\- 
H. P. motor, 
direct sys- 
tem, ammo- 
nia coils 
Consumption 
in K.W. hours 


2 

Ten-ton compres- 
sor chain -driven 
by 15-H.P. motor, 
direct system, 
ammonia coils. 

Consumption in K. 
W. hours (com- 
pressor only) 


3 

Twenty-ton com- 
pressor belt- 
driven by 35-H. 
P. motor, indirect 
system, ammonia 
coils. 

Consumption in K. 
W. hours (com- 
pressor only) 


4 

Fifteen-ton compressor 
belt-driven by 25-H.P. 
motor, indirect system, 
ammonia coils. 5-H. P. 
motor drives fan for 
circulating air with 
thermostatic control. 

Consumption in K. W. 
hours) 




(compressor 
only) 


Compressor 


Fan 


Jan., 
Feb., 
Mar., 
Apr., 
May, 








5 

193 

374 

507 

396 

387 

68 

1 




1,979 

159 










1,872 

3,056 

3,344 

3,384 

3,224 

3,264 

2,656 

936 






147 

202 

2,386 

2,228 


20 

13 

182 

351 


June, 

July, 

Aug., 

Sept., 

Oct., 

Nov. 

Dec, 


2,688 
2,876 
2,708 
2,945 
2,693 
2,550 
2,087 


3,195 
3,550 
3,390 
3,165 
2,594 
1,490 
586 


649 
535 
513 
424 
363 
204 
81 


Total, 1931 


20,685* 


21,736 


22,933* 


3,335* 


K. W. hours 
per year 
per square 
foot of sur- 
face (com- 
pressor only) 


.85 


2.57* 


1.45 


2.35* 





* Eleven months only. 

plant operated at its rated capacity only 6 1/2 per cent, of the 
time. Upon the same basis, plant 2 showed a 30 per cent, load 
factor for the month of September, and a 27 per cent, load factor 
for the seven months ending with December. Plant 3 had a load 
factor of 16 per cent, during the month of June, and a load 
factor of 12 per cent, for the period beginning with March and 
ending with October; while plant 4 had a maximum load factor 
of 21 per cent, during the month of July, a,nd 16 per cent, for 
the seven months ending with December. The load factor thus 
based upon the rated capacity, is, of course, dependent upon 
the relation of the size of the plant to the actual refrigerating 
requirements. While it is quite usual to provide refrigerating 
capacity of sufficient amount to permit of the plant being closed 



REFRIGERATION OF FURS AND FABRICS 33 

down during some 12 or 14 hours out of the 24, even at a time 
when the refrigerating requirements are at a maximum, it would 
appear that all of these plants, with the possible exception of 
No. 2, have capacities considerably in excess of those actually 
needed to meet present requirements. 

It is somewhat difficult to predict, with any degree of accuracy, 
what the consumption of electrical energy will be for a proposed 
fur storage plant unless detailed information is available as to 
the character of the insulation that is to be employed and unless 
knowledge is at hand as to the type of refrigerating plant that is 
to be installed. The method of operating the plant will also 
affect the consumption materially, as, for instance, whether 
manual or thermostatic control of the compressor is employed. 
From an examination of the data given in Table V, it would 
appear that the K. W. hours per square foot of exposed surface 
(including floor, ceiling and side walls) vary, for these particular 
plants, from a little under 1 to about 2 1/2, this variation being- 
due not only to the character of the insulation that is employed 
but to the type of plant and to the method of its operation. 

The operation of plant 3 in Table V will be briefly described 
as being typical of the modern fur storage plant. The plant in 
question is operated for about 8 months out of the year, usually 
from about March 1 to November 1, but sometimes for a 
longer period, according to the weather conditions. The storage 
vaults contain about 60,000 cu. ft., and about 15,000 fur gar- 
ments of various kinds are in storage during the summer months. 
The ammonia expansion pipes are located in a cooling room 
which contains approximately 2700 cu. ft. A system of ducts 
connects this room with the cold-storage vaults in which the 
furs are stored, and the air is kept in circulation by means of 
a blower operated by a 4 1/2 H. P. motor. Brine is allowed 
to trickle over the ammonia pipes for the purpose of keeping 
them free of frost, and the circulation of this brine is effected 
by means of a 1 H. P. motor-driven centrifugal pump. This 
brine is not employed as a secondary cooling medium, as in the 
brine system proper, but simply for the purpose stated, and in 
thus keeping the external surfaces of the cooling coils free from 
frost, the transfer of heat from the air of the cooling chamber 
to the expanding ammonia gas within the coils is facilitated, 
and the efficiency of operation is thereby increased. 

During the winter months this refrigerating plant is not 



34 ENGINEERING FOR CENTRAL STATIONS 

operated, as there are few furs in storage, and the outside air 
is sufficiently low to maintain these furs in a satisfactory con- 
dition. During this period the blower circulates the outside air 
through the vaults, which are thus maintained at a temperature 
about 10° above that of the outside air. After the plant is first 
started in the spring and until it is shut down in the fall, the 
temperature in the storage vaults is never allowed to rise above 
32° F. During this operating period the average temperature is 
approximately 20° F., ranging from 26° in the early morning to 
about 14° just before the plant is closed down in the afternoon. 
From 6 p. m., when the operation of the plant is ordinarily dis- 
continued, until 8 the next morning, when it is usually started 
again, the rise in temperature is about 12°. On Monday morn- 
ings, after the plant has been shut down over Sunday, the tem- 
perature is generally in the neighborhood of 30° F. 

The storage vaults and the cooling room of this plant are 
well insulated. The floor insulation consists of 1 in. of paving 
cement, two 2-in. layers of cork, a layer of felt, 6 in. of ordinary 
cement and finally 3 ft. of slag cement. The ceiling comprises 
1/2 in. of plaster, four 2-in. layers of cork, a 4-in. air space, and 
above this a layer of fire brick. The walls are composed of fire 
brick with cork insulation embedded in tar. From the actual 
K. W. hours consumed by this plant during the summer months, 
taken in connection with the recorded mean temperatures of the 
outside air during the same period, it would appear that the 
average loss through the floor, ceiling and walls of this storage 
vault is approximately 1.25 B. T. U. per square foot per 24 hours 
per degree difference in temperature, which shows that a high 
quality of insulation has been provided. 



CHAPTER IV 

THE APPLICATION OF MECHANICAL REFRIGERATION TO 
ICE CREAM MAKING 

Few people probably realize the present magnitude of the 
ice cream industry. The wholesale manufacture of ice cream, 
which was begun in this country by Fussell in the early fifties, 
reached an estimated yearly output of 113,000,000 gallons, 
valued at nearly $100,000,000, during the year 1911. This 
estimated factory output does not, of course, include the immense 
amount of ice cream that is manufactured by retail dealers and 
by individuals for private consumption, to say nothing of the 
quantities made and consumed in hotels, restaurants and clubs, 
and at soda water fountains, of which there are some 60,000 in 
the United States at the present time. A conservative allow- 
ance for these additional sources of production, would bring the 
total annual consumption of ice cream in the United States, 
for the year 1911, to about 138,000,000 gallons, which is equiva- 
lent to a consumption of nearly 11/2 gallons per capita of popula- 
tion. The retail value of this 1911 output, or the amount paid 
by the people of this country to gratify their taste for this 
popular dish, has been estimated at something over $194,000,000. 
At the present time, the annual output of ice cream in this 
country is increasing at the rate of about 20 per cent, per year. 

From the early days of ice cream making up to some 7 
or 8 years ago, the use of ice and salt in the freezing and 
hardening processes was universal, but the past few years have 
witnessed the introduction and rapid adoption of refrigerated 
brine and mechanical refrigeration for the purposes of freezing, 
hardening, and storing of ice cream. It is probable that the 
use of mechanical refrigeration in connection with ice cream 
making was a somewhat indirect development, for in the manu- 
facture of ice by artificial means — a development which preceded 
the application of mechanical refrigeration to the making of 
ice cream — the manufacture of ice cream was sometimes under- 
taken as a side line in order to utilize the broken pieces of ice 
which would otherwise have been wasted, and under such circum- 

35 



36 ENGINEERING FOR CENTRAL STATIONS 

stances the application of mechanical refrigeration to the making 
of ice cream was a natural, although, perhaps, a somewhat 
gradual, development. To give some idea of the rapid strides 
which mechanical refrigeration is making in the field of ice 
cream manufacture, it will be stated that, at the commencement 
of the year 1909, there were approximately 100 ice cream fac- 
tories in the United States, equipped with ice making and 
refrigerating machines. Since that time the development has 
been very rapid, and it would appear that there are, at the 
present time, in the neighborhood of 400 refrigerating machines 
in use, in this country, either for combined ice and ice cream 
making, or for the latter process alone. 

Mechanical refrigeration is at present made use of in the ice 
cream industry in one of three ways : First, it may be used only 
for freezing, hardening and storing the ice cream; second, it 
may be employed simply for the manufacture of ice, the freezing, 
hardening and storing of the ice cream then being accomplished 
by the old ice and salt method, or by the use of brine refrigerated 
by means of ice; third, it may be used directly in the manufacture 
and storage of the ice cream and, in addition, in the production 
of the ice required in the shipment of the finished product. The 
method first mentioned is followed in those places where the 
ice cream is consumed upon the premises where it is manufac- 
tured, such as in department stores, restaurants, clubs, hotels, 
soda water fountains, etc. This method necessitates the pur- 
chase of ice for packing should the ice cream be destined for 
consumption at a point requiring shipment, but it is, neverthe- 
less, frequently employed even under these conditions, particu- 
larly in the case of plants of small output. The second method 
is followed in certain cases, particularly where the manufacture 
of ice may be viewed as the primary process, the output of ice 
cream being considered as being more or less of a by-product. 
The third method is the one in which the application of mechan- 
ical refrigeration to ice cream making may be said to have reached 
its highest development, and it is the one which is usually 
employed in the larger ice cream factories, except in those 
cases where ice for shipment can be purchased at an extremely 
low price. 

The necessity which confronts the wholesale ice cream manu- 
facturer of providing ice for the shipment of his product some- 
what complicates the problem of applying mechanical refrigera- 



REFRIGERATION FOR ICE CREAM MAKING 37 

tion to both the ice and the ice cream making processes, when 
these processes are combined in the manner outlined above. 
This is due to the fact that the two refrigerating processes have 
separate and, to a certain extent, opposite requirements, which 
makes it difficult to effect an efficient combination. The manu- 
facture of ice is most efficiently accomplished with a brine temp- 
erature ranging from 15° to 18° F. The making and hardening 
of ice cream is best accomplished with brine having a tempera- 
ture in the neighborhood of 0° F., and a lower temperature is 
even more effective. If a single compressor is used for both 
processes, with a suction pressure sufficiently low to provide a 
brine temperature suitable for the freezing and hardening of the 
ice cream, the compressor output is materially reduced and its 
efficiency of operation considerably lowered; while only about 
10 to 20 per cent, of the entire refrigerating capacity is actually 
needed for the ice cream making process itself. 

In order to lessen the loss of capacity and efficiency which 
occurs when the ice making and ice cream making processes 
are on a single brine system at a temperature of 0° F. or below, 
an attempt was first made to employ brine of a higher temperature- 
ranging from about 10° to 5° F. — and in this way effect a compro- 
mise between the two temperatures most suitable for the two 
respective processes when carried on independently. The trouble 
with this arrangement is that the time of freezing and hardening 
the cream is materially increased. The temperature of the 
hardened ice cream is usually about 6° to 8° F. and with brine at 
5° F. the hardening process is considerably prolonged. On the 
other hand, a brine temperature of 10° F. freezes the ice too 
rapidly to produce the best quality of ice, but this is of no 
particular consequence in the manufacture of ice which is to be 
used for packing purposes only. It is not necessary to filter or 
distill the water from which this ice is made, and small cans are 
usually employed, which reduces the time of freezing to a few 
hours. As a result of this, the first cost of the installation is 
considerably less than that of a plant of corresponding output 
designed for the production of marketable ice, and the saving 
from this source usually considerably more than counterbalances 
any loss occasioned by the use of low temperature brine. 

An improvement upon the plan just described has been 
adopted in a number of plants. It consists of placing one or 
more of the refrigerating coils in a separate brine tank of smaller 



38 ENGINEERING FOR CENTRAL STATIONS 

capacity, from which brine is circulated by means of a separate 
pump through the freezers and setting tank. On account of 
the more rapid circulation of this brine, it has been found 
possible to maintain it at a temperature some 10° F. below that 
of the brine which is circulated through the ice freezing tanks. 

A few ice cream manufacturers have installed two separate 
refrigerating systems — one for the manufacture of ice and the 
other, of much smaller capacity, for the freezing and hardening 
of the ice cream. Such an arrangement overcomes the loss in 
efficiency which is experienced with the combined system, but 
it necessitates a considerably increased investment. It has been 
suggested that a small auxiliary compressor be employed for the 
freezer brine system, and that it compress into the suction side 
of the ice making compressor, but the authors are not aware that 
this plan has been adopted in any existing plants. 

PROCESSES INVOLVED IN THE MAKING AND STORING 
OF ICE CREAM 

It is stated by authorities that a temperature of approximately 
33° F. is necessary to retard the growth of bacteria in milk and 
cream. Moreover, in the manufacture of ice cream a much 
better product results if the cream is allowed to ripen or age. 
This ripening may be accomplished by allowing the cream to 
stand at a temperature of from 32° to 35° F. for 12 hours or more, 
or by the use of lactic ferment or cream ripening machines such 
as are used in dairies. As it is difficult to reach and maintain a 
temperature as low as 40° F. where ice alone is used for storing 
sweet cream, the need of artificial refrigeration in the treatment of 
the raw material becomes apparent. 

When the cream is in proper condition, it is taken to a mixing 
tank where the various ingredients are mixed, and this tank is 
liable to serve as an excellent breeding ground for bacteria if not 
properly refrigerated, for the use of preservatives are forbidden 
by law. 

THE FREEZING PROCESS 

From the mixing tank the mixture is carried — in some cases 
by means of gravity — to the freezers, of which there are several 
types upon the market. These may be roughly divided into 
four general classes, with several different forms in each class: 

Vertical — Ice. — This is the most usual type of freezer and, in 
the smaller sizes, is the one commonlv found in the home. This 



REFRIGERATION FOR ICE CREAM MAKING 39 

form of freezer consists of a wooden tub within which a metal 
can, holding the cream, is revolved about a vertical axis. A 
dasher, revolving in a direction opposite to that of the can, is 
placed within the can and serves to mix the contents as the can 
and dasher are revolved. The space between the wooden tub 
and the can is filled with a mixture of broken ice and salt. 

Vertical — Brine. — This type of freezer, though vertically placed, 
is sufficiently high above the floor to permit of the ice cream 
being withdrawn without stopping the dasher. The freezer itself 
is surrounded with refrigerated brine, which takes the place of 
the ice and salt used in the form of freezer first described. 

Horizontal — Brine. — This type of freezer, instead of occupying 
a vertical position, is placed nearly horizontally, the ice cream 
being withdrawn from the underside of the lower end. Refrig- 
erated brine is circulated through the annular space which sur- 
rounds the containing vessel, as in the vertical type of brine 
freezer just described. 

The preceding types are known as "batch freezers," a name 
derived from the fact that the ice cream is frozen in batches — 
each batch requiring a separate filling, freezing and emptying 
operation. The most common size of these batch freezers is 40 
quarts, or 10 gallons. The two types of brine freezers above de- 
scribed are not continuous machines, although, when provided 
with a small tank in which the next succeeding batch can be 
prepared while the preceding batch is being frozen, it is possible 
to operate these machines in an almost continuous manner. 
The continuous type of brine freezer may be designated as the 

Horizontal — Continuous — Brine. — This type of freezer is radi- 
cally different from any of the types that preceded it and which 
have been described very briefly above. In thi3 machine 
the mixture goes in at one end and the finished ice cream comes 
out at the other end. The freezing process is accomplished by 
means of brine which circulates through discs which revolve 
rapidly and force the cream through the machine. Besides 
being continuous in its action, this machine possesses a secondary 
advantage in being open, which affords the operator much better 
control over the freezing process. 

The use of these brine freezers is not necessarily confined to 
those plants which employ mechanical refrigeration. Brine, 
made from ice, salt and water, may either be provided in a large 
tank and circulated by a pump through a number of freezers, 



40 ENGINEERING FOR CENTRAL STATIONS 

or a brine box may be obtained with a single freezer and the 
brine circulated by means of a small pump. 

In considering the process involved in the freezing of ice cream, 
the question of "swell" presents itself, and it is of sufficient 
importance to be gone into in some detail. The term "swell" 
is applied to the increase in volume which the mixture undergoes 
during the freezing process. This increase in volume results 
almost entirely from the incorporation of air into the mixture 
during the period of freezing, and the degree to which it takes 
place depends upon a number of conditions. The viscosity of 
the cream from which the mixture is made affects materially the 
amount of "swell"; the more viscid the cream is, the greater is 
the amount of swell during the freezing process, other things 
being equal. As the viscosity of cream increases very consider- 
ably from the time of its separation for several hours, and then at 
a slower rate for several days, especially if held cold, the desira- 
bility of storing, and at the same time refrigerating, the raw 
cream becomes apparent. 

The rate of freezing has been found to have an important 
bearing upon this increase in volume. If the freezing is done 
too rapidly, the time interval during which the cream passes 
from a condition which will permit of its being thoroughly beaten 
without turning to butter to a condition of being thoroughly 
frozen, is too short to permit of a proper increase in volume. 
Experiments made by the Vermont Agricultural Experiment 
Station show that the expansion in volume takes place during 
a drop in temperature of only a few degrees, and that if the 
cream is frozen too rapidly, insufficient time is available, while 
passing through the few critical degrees of temperature, for the 
proper amount of swell to take place. It was found that the 
ordinary mixture of cream and sugar used in ice cream making 
was too thin to retain any appreciable amount of air prior to 
its reaching a temperature of about 34° F. At this temperature 
it begins to foam up slowly and to increase gradually in volume 
until a temperature of 29° to 28° F. is reached, the true freezing- 
point usually lying between these two temperatures, but varying 
slightly with the amount of sugar used in the solution. At this 
point the temperature remains constant for a short period, 
during which time the latent heat of the cream is being abstracted. 
At 28° to 27° F. the frozen product is ready to remove from the 
freezer. It appears, therefore, that a freezer should not be 



REFRIGERATION FOR ICE CREAM MAKING 41 

operated at a high speed until a temperature of approximately 
34° F. is reached, as the mixture does not begin to swell until this 
temperature is attained and there is danger of the cream "butter- 
ing" prior to its being cooled to a point below the churning tem- 
perature. When a freezer is operated by an individual motor, 
or is otherwise susceptible to speed control, the initial speed 
should be moderate until a temperature of 34° F. or thereabouts 
is reached, this being followed by a considerably higher speed 
while the temperature is passing through the critical stage during 
which the swell occurs. The speed should then be reduced to 
prevent a loss of swell while the ice cream is being further cooled 
before its removal from the freezer. 

Probably many will be surprised to know that ice cream, 
when manufactured commercially, is not, as a rule, frozen hard 
in the freezer, but is removed in a condition that permits of its 
being poured with comparative ease, the consistency usually 
being about that of condensed milk. 

The time required for the freezing process with the ice and 
salt method, and with the ordinary 40-quart freezer, depends 
upon the temperature of the mixture entering the freezer and 
upon the size of the pieces of ice and upon the quantity of salt 
which is present. The addition of water to the ice and salt 
increases the surface of contact between the cold-producing 
medium and the can, and hence hastens the freezing process. 
It is claimed that when the mixture enters the freezer at from 
60° to 65° F. it should not be frozen in less than 20 minutes, and 
that it should not require more than 25 minutes; when started 
at 45° F., from 12 to 16 minutes should be allowed, while when 
started at a temperature of 34° F. it may be very satisfactorily 
frozen in 8 to 10 minutes. In the ordinary ice cream manu- 
facturing plant using ice and salt for freezing and 40-quart cans, 
and with the mixture entering the cans in the neighborhood of 
40° F., four batches are commonly frozen in 1 hour, 12 minutes 
being the time usually allowed for freezing each batch and 
3 minutes for changing cans and renewing the ice and salt. In 
order to increase the amount of swell, the time of the freezing- 
process is sometimes still further prolonged, resulting in only 
three batches per hour. With the brine type of freezer, the 
time of the freezing process is considerably reduced, as the tem- 
perature of the brine is more uniform and usually carried con- 
siderably below that normally obtained with the ice and salt 



42 ENGINEERING FOR CENTRAL STATIONS 

mixture. As a result of this, six or seven batches per hour are 
frequently obtained with brine freezers without unduly sacri- 
ficing the amount of swell. 

THE HARDENING PROCESS 

After the ice cream is removed from the freezer, it is taken to 
a setting tank or hardening room and subjected to a temperature 
of about 0° F. for several hours until it becomes thoroughly 
hardened. The old method of hardening consisted of placing 
the ice cream in cans or other containers and keeping it buried 
in ice and salt until ready for shipment. This method is still 
largely used, and the ice cream is sometimes kept in this manner 
for as long as 8 hours, with frequent renewals of ice and salt 
before it is shipped. This method is not only expensive as 
regards material and labor, but its use makes it difficult, if 
not impossible, to maintain sanitary surroundings. 

Another method which has been employed for some time is 
known as the submerged system, and consists of placing the ice 
cream, usually in 10-gallon cans, in an insulated tank containing 
calcium chloride or sodium chloride brine, this tank usually being 
similar in structure to a small ice-making tank. Sometimes 
ammonia coils are placed in the setting tanks, and, when the 
tank is of especially large size, means are provided for circulating 
the brine. Undoubtedly the best practice at the present time, 
when employing a brine tank for hardening, is the use of a shell 
cooler. With this arrangement the freezers are frequently placed 
on the same brine circuit with the setting tank, and brine is 
circulated by means of a small pump. The setting tanks are 
generally provided with an iron frame-work over the top to hold 
the cans in place, and especial care is taken to prevent the brine 
from entering the cans. The chief objections to this method of 
hardening are to be found in the very considerable operating 
expense that is occasioned by the large exposed surface of the 
tank and the usually insufficient insulation provided for the low 
temperature that is carried; in the danger of the brine gaining 
access to the cans, and to the dffiiculty of maintaining the sur- 
roundings in a sanitary condition. A more recent method of 
hardening, known as the dry-air system, has been installed in a 
number of plants and eliminates many of the objectionable 
features of the brine tank and the ice and salt methods. In this 
system a small, well-insulated and vestibuled room is maintained 



REFRIGERATION FOR ICE CREAM MAKING 43 

at about 0° F., either by means of brine or ammonia expansion 
coils located in a loft or bunker separated from the storage 
space by a false ceiling. The ice cream, in cans or other forms 
of containers, is usually placed upon shelves running about the 
room and a revolving fan is provided to keep the air in circu- 
lation. This method possesses the very decided advantage of 
cleanliness, and permits of the cream being handled in bricks, 
which greatly adds to the convenience of handling and packing 
the finished product, besides avoiding the loss through shrinkage 
which occurs when ice cream is repacked into pint, quart and 
gallon containers after having once been hardened in cans. The 
loss of volume incurred by this transfer is frequently as great 
as 10 per cent. The economy of this method of hardening 
naturally depends upon the quality of the insulation that is 
provided, but if this matter is given proper attention, this 
method of hardening is undoubtedly the most satisfactory one 
that can be employed at the present time. 

Six or eight hours is the usual length of time allowed for the 
hardening of ice cream by means of the ice and salt method. It 
is stated that soft ice cream will become medium to medium 
hard in about 6 hours in the ordinary commercial setting tank 
in 40-quart units with a mixture of ice and salt, provided ordi- 
nary attention is paid to the renewal of the ice, and that it will 
fall about 2° F. in the following 2 hours, thus making 8 hours 
sufficient time to produce hard cream if careful attention is 
paid to the temperature of the brine and its maintenance. A 
difference of a few degrees in temperature affects materially the 
time required for hardening, which is also affected by the size 
and shape of the receptacle in which the ice cream is placed, 
to say nothing of the method of hardening which is employed. 
With brine of extremely low temperature, the time of hardening 
may be reduced to as small an interval as 2 hours, although such 
a procedure affects quite appreciably the character of the product. 
Some manufacturers will not ship any ice cream that has not been 
hardened for at least 10 hours, and it is probable that some 5 or 
6 hours is the shortest time interval which should, as a general 
rule, be allowed for the hardening process. 

THERMAL PROPERTIES OF ICE CREAM 

Prior to the investigations conducted by Mr. Joseph H. Hart, 
the results of which are to be found in Ice and Refrigeration, 



44 



ENGINEERING FOR CENTRAL STATIONS 



Vol. 34, there was a little reliable data available upon the 
thermal properties of ice creams and water ices. The investi- 
gations referred to were conducted for one of the refrigerating 
machine manufacturing companies, in order to determine, among 
other things, the theoretical amount of refrigeration required for 
ice cream making. Tests were also made to determine the tem- 
peratures of orange ice and of several different flavors of ice creams 
under different conditions of hardness. A cream or ice was con- 
sidered as being hard when a thermometer could be pushed into 
the mass with difficulty and with some slight danger of breaking 
the bulb of the thermometer. It was considered as being 
medium, when the thermometer would stand unchanged in 
position, and as being soft when the thermometer would gradually 
sink into the mass of its own weight. Table VI shows the 
results obtained in these temperature tests. 



TABLE VI. 



-TEMPERATURES OF ICE CREAMS AND ORANGE ICE 
IN DEGREES FAHRENHEIT 





Vanilla 


Peach 


Choco- 
late 


Straw- 
berry 


Orange 
ice 


Hard 


9 
15 

18 


9 
13 
16 


10 
14 

18 


8 
13 
17 


6 

10 
14 


Medium 

Soft 



The most important data secured in these investigations are 
summarized in Table VII. From the last line in this table, it 
will be seen that it is theoretically possible to change approxi- 
mately 12 gallons of liquid ice cream per hour into the hard com- 
mercial product per ton of refrigeration. The number of gallons 
of hard product produced will, of course, depend upon the amount 
of "swell." If the "swell" is 100 per cent. 24 gallons of hard 
product could theoretically be produced per hour per ton of 
refrigeration; if the "swell" is only 60 per cent., approximately 
20 gallons of hard ice cream could be obtained. Due to radiation 
and other losses, these figures are, of course, not obtainable under 
the conditions that are met with when ice cream is produced on 
a commercial scale. The number of gallons of finished product 
produced per day per ton of refrigeration depends upon a con- 
siderable number of variables, and it seems to differ very 



REFRIGERATION FOR ICE CREAM MAKING 45 
TABLE VII 

















\ anilla 


Peach 


Chocolate 


berry 


Orange ice 


Mean specific heat of liquid 


.74 


.80 


.79 


.77 


.70 


ice cream, 70° F. to 40° F. 












Total heat, 32° F. to 9° F. in 


S4 


72 


74 


81 


122 


B. T. TJ. per pound. 












Total heat, 70° F. to hard con- 


110 


104 


106 


113 


176 


dition in B. T. U. per 












pound. 












Specific weight at 75° F., or 


1.095 


1.082 


1.089 


1.095 


1.176 


weight in grams per cubic 












centimeter. 












Weight in pounds per gallon 


9.123 


9.024 


9.082 


9.123 


9.808 


of 231 cu. in. 












Total heat, 70° F. to hard con- 


1003 . 5 


938.5 


962.7 


1031. 


1726.2 


dition in B. T. U. per gallon. 












Theoretical gallons of liquid 


12 


14 


13 


11 


7 


ice cream changed to hard 












commercial product per ton 












of refrigeration per hour 












(approx.) 













materially in the case of different plants, some of which claim 
outputs as high as 200 gallons per day per ton of refrigeration, 
while others are rated as low as 50 gallons per day per ton. It 
all depends, of course, upon the efficiency of the plant, the rate 
at which it is being operated, and the number of hours per day 
the plant is in operation. 



«t 
































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6 10 14 18 22 26 

Capacity in. Tons of Refrigeration 



30 



Fig. o. — Cost of motor-driven refrigerating plants for ice cream making. 
COST OF REFRIGERATING PLANTS FOR ICE CREAM MAKING 

Fig. 5 shows the approximate cost of motor-driven refrigerating 
plants for ice cream making. The cost figures, as given, cover the 



46 



ENGINEERING FOR CENTRAL STATIONS 



complete equipment, including hardening and raw cream 
storage rooms, but they do not include any ice making equipment. 
When the ice cream manufacturer is to make his own ice for 
shipping purposes, a considerable portion of the refrigerating 
capacity would, of course, have to be devoted to this purpose, 
thereby reducing the amount of refrigeration available for ice 
cream making. The cost of the necessary ice making equipment, 
would increase the cost of the plant, as shown in Fig. 5, by only 
some 2 or 3 per cent, on the average. 

CONSUMPTION OF ELECTRICAL ENERGY IN ICE CREAM 
MAKING 

Fig. 6 shows the yearly consumption in kilowatt hours plotted 
against the refrigerating capacity in tons for several motor-driven 
refrigerating plants used for ice cream making. The mean 



36*000 


































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S 30,000 

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12 3 4 5 6 7 

Capacity of Plant in Tons of Refrigeration 



Fig. 6. — Showing the consumption of electrical energy by small motor- 
driven refrigerating plants employed for ice cream making. 



consumption of electrical energy per year per ton of refrigerating 
capacity is seen to be about 4500 kilowatt hours. If we assume 
a connected load of 1.5 kilowatts per ton of refrigeration, the 
average number of hours of use per year of the rated refrigerating 
capacity is seen to be 3000, which is equivalent to a yearly load 
factory of about 34 per cent. Fig. 7 shows the monthly variation 
in the refrigerating requirements of these same plants expressed 
as a percentage of the total yearly requirements. It will be 



REFRIGERATION FOR ICE CREAM MAKING 47 

seen that the maximum requirements occurred during the month 
of July, and that the average requirements during this month 
were over 13 per cent, of the total for the year. During this one 
month, therefore, the total rated capacity of these plants, was in 
use for something over 50 per cent, of the entire time. Fig. 7 
also shows how desirable ice cream making is as a central station 







































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Fig. 7. — Showing the monthly variations in the refrigerating requirements 
of ice cream manufacturing plants. 

load. The heavy full-line curve represents the output by month 
of a large central station expressed as a percentage of the total 
yearly output. It will be seen that this curve reaches its lowest 
point at a time when the refrigerating requirements for ice cream 
making are at a maximum, and that its highest point coincides 
with the point of minimum refrigerating requirements. 

MOTER-DRIVEN ICE CREAM FREEZERS 

The following table shows the size of electric motor that is 
usually employed for direct connection to "batch" ice cream 
freezers of the sizes mentioned: 



Capacity of Freezer 

in gallons 

5 

10 

15 

25 



H. P. of motor 

3/4-1 

1 1/2-2 

3 

5 



In the case of continuous freezers, one manufacturer recom- 
mends the sizes of motors given below when each freezer is 
equipped with its own individual motor. These motor sizes are 



43 ENGINEERING FOR CENTRAL STATIONS 

undoubtedly liberal, and motors of somewhat smaller capacity 
are sometimes employed. When a single motor operates a gang 
of these freezers, a considerably smaller horse-power allowance 
per freezer is commonly made. 

Capacity of freezer in 

gallons per hour H. P. of motor 

30-40 3/4 

50-70 11/2 

80-100 2 

100-130 2 1/2 

150-200 3 



CHAPTER V 

COST OF GENERATING ELECTRICAL ENERGY IN 

STEAM-DRIVEN CENTRAL STATIONS OF SMALL 

AND MEDIUM SIZE 1 

In view of the very large number of central stations of small 
and medium size scattered throughout this country, some figures 
showing the actual cost of producing a kilowatt hour in a number 
of stations which come under such a classification, should be of 
interest. 

The figures herein presented are believed to be authentic, 
inasmuch as they have been obtained from reliable sources 
which give not only the cost of operation in detail but consider- 
able information regarding the type of equipment as well. 
While the stations which have been selected have a yearly output, 
as measured at the switch-board, of less than 9,000,000 kilowatt 
hours, it is not the intention of the authors to use this figure 
as the dividing line between central stations of medium and of 
large size, for if it were so used, it would be difficult to properly 
classify our few really large central stations which have yearly 
outputs running into the hundreds of millions of kilowatt hours. 

Fig. 8 shows the total cost per kilowatt hour generated — in- 
cluding such items as fuel, labor, repairs, supplies, etc. — plotted 
against the total number of kilowatt hours generated for some 
20 odd central stations. These stations not only vary consider- 
ably in size, but also as regards the nature of their equipment. 
While all of these plants are operated condensing, some of them— 
particularly the smaller ones — are still using belt-driven gener- 
ators of comparatively small capacity. Bituminous coal, 
ranging in price from $2.75 to $5 per gross ton, is used almost 
exclusively, although in a few of the plants a certain amount of 
coke, coke-breeze or screenings is used. With the exception of 
one plant, the boiler are all hand-fired. 

It will be observed that those plants in which turbine units 
have been installed show no lower cost of operation than the 

1 This chapter first appeared as an article in the Electrical World, Vol.57, 
p. 548. 

4 49 



50 



ENGINEERING FOR CENTRAL STATIONS 



reciprocating engine plants of similar output, which is not alto- 
gether surprising for plants of the capacities shown. The 
lessened cost per kilowatt hour with increased yearly outputs, 
is of considerable interest, and it is evident that one cent per 
kilowatt hour at the busbars is about the lowest unit cost that 
may reasonably be expected with present types of steam-driven 
equipment — until a yearly output in excess of some 10,000,000 
kilowatt hours is reached. Fig. 8 shows that the variation in 
cost per kilowatt hour with the output is substantially hyper- 
bolic in character, and may be expressed by the formula F = 1 + 

Y — This hyperbola is shown by a dotted line, and it is 

evidently asymptotic to an X axis drawn through 1 cent per 
kilowatt hour. Of course, this relation does not hold good for 
greater yearly outputs than are shown in Fig. 8, for the cost per 






Sfc 






ft x 



3 




x 




















i i i i i 


























o Reciprocating Steam Engines. 
• Steam Turbines. 
X Mixed Equipment - Engines 
and Turbines. 

Equation of Uyperbolic Curve. 

Y-1+ ^f 






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en 




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^ 123456789 

Millions of Kilowatt Hours Generated per Year 

Fig. 8. — Showing the relation of cost per K. W. hour to yearly output in 

K. W. hours. 



kilowatt hour soon falls below the 1-cent line as the yearly 
output is further increased, and it becomes 1/2 cent or less in 
stations of very large output. 

While the load factor should, and undoubtedly does, have a 
considerable influence upon the cost of producing a kilowatt hour, 
the variation in unit cost does not follow the variation in load 
factor with any degree of closeness in the stations herein cited. 
While the load factor increases in a general way with the output 
in kilowatt hours, or with the size of the central station, due, as 
a rule, to an increase in the connected motor load, Fig. 9 shows 
that such increase is not at all uniform for the plants herein 
considered. The load factor percentages shown in Fig. 9 are 



COST OF GENERATING ELECTRICAL ENERGY 51 



based upon the rated capacities of the stations, as the maximum 
hourly outputs were not available in all cases. When based 
upon the maximum outputs, the yearly load factors would aver- 
age some 10 per cent, greater than the figures which are given. 



3 24 














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1 12 








































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2 S 4 5 6 7 

Millions oil Kilowatt Hours Generated per Year. 



Fig. 9. 



-Showing the relation between load factor, based upon station 
capacity, and yearly output in K. W. hours. 



( 








_r_ 


1 




























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JSawll Belt-driven 

( Lnits 
























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*( Screenings Forms S0$ of Total Fuel turned 








































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1234567 89 

.Millions of Kilowatt Hours Generated per Year, 

Fig. 10. — Showing the relation between the consumption of coal per K. W. 
hour and the yearly output in K. W. hours. 

The highest load factor for any of these stations, based upon 
rated capacity, is about 23 per cent., and the lowest, 11 per cent.; 
while the average is approximately 17 per cent. 

The reduction in the cost per kilowatt hour as the yearly 



52 



ENGINEERING FOR CENTRAL STATIONS 



output in kilowatt hours increases, is, of course, due to the 
smaller coal consumption per kilowatt hour which, as a rule, 
obtains in the larger stations, and to the lower labor costs per 
unit generated. Fig. 10 shows the consumption of fuel per 
kilowatt hour in these same plants. While the consumption 
of fuel per unit generated very evidently varies inversely as the 
output in kilowatt hours, this variation is not altogether uniform, 
due, primarily, to differences in the quality of the fuel which is 
burned and to the different types of equipment which are in use. 
It is evident that 3 lb. of coal per kilowatt hour may be con- 
sidered to be a minimum figure for steam plants with an annual 
output not exceeding some 10,000,000 kilowatt hours. In very 
large stations, of course, this figure may become 2 lb. or even 
less. 



280 

260 

240 

§220 

^200 

9) 

a 180 

1 160 

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120 

100 



















































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1000 



2000 3000 4000 5000 
Station Rating in Kilowatts 



6000 



Fig. 11. — Showing the relation between the K. W. of station rating per 
man employed and the size of the station in K. W. 



Fig. 11 shows the number of kilowatts of rated station capacity 
per man employed, power-plant labor alone being considered. 
The abscissae represent the rated capacities in kilowatts of the 
same stations whose outputs are shown upon the other charts. 
It is interesting to observe how the number of kilowatts per man 
increases as the stations become larger in size. As a result of 
this, the labor cost per unit generated becomes progressively 
less as the capacities — and outputs — increase. The lowest cost 
of labor per kilowatt hour for the plants herein considered, is 
slightly below 1/4 cent, and the highest cost is slightly above 
11/2 cents; the average labor cost per kilowatt hour generated 
for all of the plants is .43 cent. 

Fig. 12 shows the percentage relations of the cost of fuel and 
of labor to the total operating cost. It is evident that these 



COST OF GENERATING ELECTRICAL ENERGY 53 

relations are in no way affected by the annual output in kilowatt 
hours. The average percentage which the cost of fuel bears 
to the total operating cost is found to be 55.7; while the average 
percentage for labor is 27.8. The average of these two items 



S 60 
O 

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3 20 

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Cost of Labor 
Average 27.82$ 






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f 






V 


























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V 


































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Cost of Fuel 
Average 55.70$ 





















































































































12345678 9 

Millions of Kilowatt Hours Generated per Year 
-Shoeing the percentage relations of the cost of fuel and the cost 
of labor to the total cost of generation. 



combined, is, therefore slightly over 83 per cent., which leaves 
an average of a little less than 17 per cent, of the total operating 
cost to cover such items as repairs, supplies, etc. The average 
ratio which the cost of fuel bears to the cost of labor is approxi- 
mately two to one. 



CHAPTER VI 

KILOWATT HOUR COSTS IN STEAM-DRIVEN GENERATING 

PLANTS 

In the preceding chapter it has been shown that the total cost 
of generating electrical energy at the busbars, exclusive of all 
fixed or overhead charges, is, roughly, a hyperbolic function of 
the total number of kilowatt hours generated per annum, at 
least in the case of some 20 odd central stations, with yearly 
outputs ranging up to approximately 9,000,000 K. W. hours. 
At approximately the yearly output mentioned, the kilowatt 
hour cost appears to approach 1 cent for the average modern 
steam-driven central station generating plant. 

In order to compare the various items that enter into the cost 
of generating electrical energy in steam-driven generating plants, 
the authors have prepared the accompanying table, Insert 1, which 
shows the itemized operating costs of 28 such plants located 
in the United States. The yearly outputs of these plants range 
from less than 1,000,000 to over 31,000,000 kilowatt hours. In 
certain instances the operating costs for 2 or more years are 
given in order to show the effect of a change in the type of gener- 
ating equipment or of an increase in the output upon the cost of 
generation. With the exception of some three or four cases 
where the figures apply to electric railway plants, the operating 
costs, as given in the table, are those of central station generating 
plants. 

As the type of generating equipment has a very important 
bearing upon the cost of generating electrical energy, a brief 
description of the generating equipment is given in the case of 
each plant. The load factor, as based upon the rated capacity 
nd upon a year of 8760 hours, is given in each instance, and the 
true load factor — that is, the ratio of the average to the maximum 
load during the year — is given wherever it has been possible to 
ascertain the maximum load on the plant. The kind of fuel 
burned, together with its cost per ton, is given for each plant 
with one or two exceptions, as these two items affect very materi- 
ally the cost of fuel per kilowatt hour generated. As the amount 

54 





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1 Typ» of Generating 


Ifjj" 


ESEs 


-US* 


I 


ct..per H3E," "A' %&&• K 


s'S* 


1 J Equipment. Capaci 


3? 


- ■"= " "Ine 


' K ' na 


fin 


J°Hr 


KKhr Unployed 


K: R» SE S3 «.« T«ai '7 »*■ »•"■ rl; 


1 


Turbo-alternator. 


16,500 


31^17,30 


31. 








>3.51 3.39 


.41 






.697 


3 


Turbo-alternatbre 


8,000 




23687,80 


33.6 






S-" 3.K 
3. KB 


.366 


H 




•XL 


Jj 


i - alooo k.' w.° 


6,000 


6,000 


19,751,30 


37.6 37.6 *'"° 

19.045 anthraci 


° »•" 3.5 


„. 7 Engineers, o 3w.?d.llen 

5 ' 4 25 Poilor Hm.Men.30 Coal .239 .0066. 


23 .0296.0018 .004 .033 .66 


4 ' 


ed engine unite, condensing 


3,500 




10,060,61 




12.15C 


Pituminoi 


s 4.80 3.7 


58 9 Firemen 


II . 155 


.051 .035 


.83 


5, 


^/ff^fHI^rlvE' 


3,000 




5,498,74 


30.9 




Coke 

'"BrSSSS 1 


e 3^50 


56 9 Engine Room and 


H .33 .065 . 


54 .037 .156 .055 .011 


1.10 


J - 


1-1500 K.W.Iurio-altarnator; 


6,300 




6,053,616 


13.0 








1 3.17 


63 7 Firomen. 7 3team & 


H .30 .366 . 


59 .074 .40 .068 .014 


1.41 


50 


4 Cpp, engines; 1-500 K.B.and 


5,000 




8,316,367 


ia.8 




9,86- 


Pitumlnou 


s 3.35 


6 Engineers, 9 Firemen 
54 8 3tean and Electrical 


H .38 .173. 


65 .074 .31 .049 .013 


1.2 ! 


51 


4 sngineadrivlng 15leneratonj 


6,000 




8,776,165 


16.7 




13,50, 


: 1 




b Engineers, U Firemen 
61"! 8 Btean & Electric 
Attendants 


H .396 .147 .046 .053 .344 .04 .013 .001 1.31 


Of 


4 direct-connected onglne 


5,000 


3,350 


8,800,838 


=0.0 


30.0 


12,118 


Bitoitinou 




3. Of 


fc» Knglneers, 4 Oilers 
42 6 Firemen, 3 CoalPasBei 
4 3w. Bd. lien 


s .38 


.39 .99 


CA 


Turbo-altornntoM 


3,000 


3,510 


5,858,356 


22.3 


36 . 6 


3,1=0 


do. 


4.4 


3.10 


<» i &T 3 ' 4 0Il8ra 

3 Ooal Passers 


H .39 .051 .0033 ..0533 .097 1.06 


61 


do. 


3,000 


3,750 


8,079,038 


30.7 


33.6 




do. 


4.3 




4 Engineers, 3 Ollera 


H .33 .039 .007 .031 .067 005 .008 .037 .69 




'iisi^irtiWHar^ 


5,200 


3,100 


7,344,392 


10.1 


37.0 




Pituntnou 


3.5 




4 Engineers, 5 Firemen 
43 3 Oilere.3 Ooal Passers 


H .30 


.33 


■9*1 


U 


IflSKs:™^- 


4,500 




5,764,368 


1-1.6 










3.34 . 


68 21 Total 


H .34 


.23 


1.35: 


81 


do 


4,500 




7,126,314 


18.1 










3.16 . 


63 33 Total 


H .38 


.13 


1.03 


11 


and 1 - 3,000 H.P.Cdop.Cond^ 


5,000 




6,043,204 


13.8 






Bitumlnou, 






4 Engineers, 3 Oilers 

688 1 Wiper, 2 Ooal Hassers 

4 3w.9d.«en,6 Firemen 


H .346 .069 .0 


15 .02 .134 .054 .018 


1.33 


' w 


3 Comp.Cor.d. Engine Units of' 


3,400 


1,660 


4,716,000 


14.7 


33.6 


1,000 


mjumino* 


1.7: 


3.33 . 


b Engineers, 2 Oilers 
3 Firemen. ""Slpd. Hon 


11 .31 .073 .01 


4 .023 .109 045 .03 031 


1.06 




balance of," equipment comp'. 


3,400 


1,980 


5,613,03< 




31.8 




»•— 


3.9 




3 Firemen, 3 Si". 9d. lien 


U .35 


26 


1.05 


11 


aggregating 3,900 H.F; 1 - 
1600 g.W.Turho-^ltematoT 


4,000 




5.400.00C 


15.4 






do. 


4.7 


3.26 . 


70 1£ Station Attendants 


H .36 


034 


1.24 


13 


Turbo-alternators 


3,500 


1,960 


4,673, 25C 


=2.2 


36,4 




do. 


3.3. 






.35 


.33 


.99 


13/ 


belted generators 


3,600 




3,106,000 


14.2 






do. 


4.51 


3.30 . 


4 14 Total 


.41 .158 .01 


1 .034 .303 .037 .025 


1.41 


131 


do. 


2,500 


1,625 


4,462,551 


=0.4 


31.3 


6,993 


8™™ir,S 


4.76 




" 3 Engineers, 3 Firemen 
4 3 Cleaners, 3 CoalPaa3ers 


H .326 .176 .01 


i .06 .239 .034 .034 


l.se 


14* 


direct-connacted .eneratore 


3,000 


1,210 


3,288,622 


18.8 


31.0 




Coke 




4.39 . 




H .30 .083 .00 


.066 151 .038 .019 


1.43 




do. 


2,000 


1.510 


4,006,157 


32.9 


30.3 


3,700 

= .650 


Bituminous 




3.'66 . 


.4 Engineers, 3 Oilere' 


H .31 .041.07 


.017 .13 .025 .016 .024 


1.34 


LW 


do. 


2,000 


1,650 


4,461,580 


35.4 


30.3 


1 ,57 3 


Bituminous 


4.31 


8.52 . 


T | Clemen"' * ° U " B 


H .29 


.11 


1 07 




Turbine Onlto 


2,000 




4,410,295 


35.3 














.20 


" 03 


.73 




[t'CuT^'i^r^S;!" 


2,300 


1,375 


3,7=1, ,53 


18. D 


35.4 


6,076 


Cumberlana 
Bituminoui 


3.97 


3.6 .6 


5 3 Sf.;r."- C s.rffls,. 


EOJE 

H .28 .073 .019 


.063 .155 003 .019 .04 


1.16 


m 


Engine-driven units ' - ao^TT- 
atora belt-driven and direct- 
connected - moatlv the latta* 


2,600 


1,950 


4,408,965 


18.0 


35.8 


lOFi 






3.77 .8 


05 | OiKri's^dfSSn 8 " 


K .355 .055 .018 


.033 106 .015 .021 


1.20 


1,965 




3,990,634 


=3.3 








4.31 




3 Engineers 


H .34 .068 .038 








neoted .„«!„..,»,„.„ „„,♦.■ 


2,435 


1,000 


4,357,648 


20 4 


=6.2 




No. 3 




.7 


3 Engine'ers 
3 Firemen 


H .33 .068 .015 


.014 097 .016 .017 ,018 


1.16 


19 
20A 


rs^jiKs-'"' - ™°°& 


2,156 




4,306,000 


33.8 




- ,',,'.- 




33( 


3.53 .8 


6 I &Ii n ?f.£., 5 Flram6n 

6 Helnere 


H .334 


.17 


1.27 


2 - Engine-driven unite 
■i-VoO Kir Turbine unite, 3 cond 
SStiSVf'!! 1 ? 8 3 ""-eot-con- 


2,339 




1,928,068 


= 3.4 




136 




2.59 


1.12 .8< 


3 Fifane""; CoaVrasee, 


H .34 065 039 


.007 .101 .005 .013 


1.28 


20i 




2,330 


1,450 


3,137,800 


10.4 


ice 


3.77B 




3.87 


.96.09 


~^T 


H .31 046 .003 


.013 .069 .001 .009 .012 


1.37 




■ 


2,339 


1,200 


3,428,940 


11.8 


23.1 


4,230 


""-*— 


3.90 


.90 .68 


do. 


H .39 








'i™ioctlj"?enor" , or» re ' :t " 


1.400 


1,200 


2,089,200 


17.1 


19.9 




Pituminois 


S.K 


.57 


3 Engineers 


H .30 077 


.051 .07 




" 




1,250 




1,470,066 


13.4 






Bituminoui 


4.7S 


.62 .82 


4 4 Firemen" 


H .466 096 .007 


.064 .167 .07 .05 


.66 


... 




1.350 




1,602,371 


14.7 




:■ . 300 


■ V ;-■.!-:' ,i.:. ;;, 


3i36 


.61 .70 


4 «?eSen" 


H .48 


" .36 1 


.54 




j;jQ a-44KH.Rri.nl, .... ||r .[| ' 


583 




1,040,38= 


30.4 






"o; HIT' 


.,39 
S.00 




3 Engir.eere 

1 D v r..-u-:o Tender 




005 .096 .078 ..026 1 


71 


"" 


.00 K.». Turbine iJnit 


1,063 




1,227,61, 


15.0 






SI? Mtu. 


3.00 




do. 


H .69 .168 .011 


006 .186 .083 .031 1 


96 




do. 


1,062 




1.479,898 


».• 






7,1 Oca 


;.36 
1.97 


1.0 


do. 


H .59 .337 .017 


009 .353 .084 .026 3 


05 


... 


do. 


1,092 




1,466,045 


15.5 




3,054 


nL : ?:-.-,..: 


> 




dO. 


H .61 


.47 2 


04 


" 




800 




1, .40.173 


16.3 




2,465 


itumincu: 


;.==■ 


.87 .91 


2 EngirieTTFT 


H .49 




54 




direct-connected en,.,,, u, !ts 


950 




931,640 


11.1 




,.:>3 


croc:,',:."! 


CO 


•49 1.0 


3 Engineers 

4 Firemen 


H 1.63 .176 .047 


046 .371 .116 .038 3 


j . 






376 




650,680 


••» 




,4U 


i.^inou, 


4.6! 8 




f Jifr" 9 


H .726 .102 .067 


106 .277 .038 .0S5 2 


69 




^ratora'-^" " 1 


725 




886,800 








it Mm , 


'■* 


.49 1.3 


1 fife'SIn" 


H .71 .103 .016 


032 .151 .025 .032 2 




' 


do. 


735 




689.760 






-■ 


lo. 


! 


79 1.3 


3 Engineers 


K .76 .13 .003" 


045 .178 .508 .025 2. 


33 




s&idp?* *& ** 


906 


487 


678,140 


1.0 


O.C 


,750 


do. 1 


. 74 8 


54 l.lt 


4 Er. fi inaere, 1 Oiler 
3 Firemen 


H .515 .169 .03 


021 .22 .005 .095 2 


„„ 


" 




630 




730,458 


3." 




.553 


do. | 


. IS 4 


99 .925 


3 Engineers | 

3 Firemen | " - c85 ■» -00M 


1135 0155 .061 1. 





KILOWATT-HOUR COSTS IN STEAM-DRIVEN GENERATING PLANTS 








n, i 






KILOWATT HOUR COSTS 55 

of fire-room labor required depends largely upon whether the 
firing is done by hand or by mechanical means, a column has 
been provided to show which method of firing is employed. The 
various items of cost given at the heads of the several columns 
in the table do not appear to require any explanation, with the 
possible exception of the item "Miscellaneous Costs per Kilowatt 
Hour." This item includes all costs of generation which do 
not appear in any of the preceding columns. In some cases it 
includes all costs except those of fuel and labor; in other cases 
it may cover perhaps only some single item of cost, the relative 
importance of which is very slight. In every case it represents 
the difference between the total generating costs per kilowatt 
hour, as given in the final column, and the sum of the items of 
cost appearing in the preceding columns. 

The authors will first comment briefly upon a few of the more 
important points disclosed by this tabulation of operating data, 
an this will be followed by a short description of the charac- 
teristic features of the several plants. 

In studying the accompanying table, one is perhaps first of all 
impressed by the very considerable differences which are seen 
to exist in the operating costs of plants in which the generating 
equipments and the conditions of operation are very much the 
same. Observing first the relation of the maximum load to the 
total generating capacity in kilowatts, it will be seen that the 
ratio of the former to the latter varies all the way from 100 per 
cent, to less than 50 per cent. This variation is not at all sur- 
prising when one considers that some of the plants contained in 
this list have been designed to take care of a connected load 
which has not as yet been commercially developed. The load 
factor based upon the rated capacity shows a similarly wide 
amount of variation, but the true load factor — or that based 
upon the actual maximum load upon the plant during the year — 
shows a considerably higher degree of uniformity. Excluding 
those plants which furnish electrical energy for the operation of 
electric railways — which usually possess a higher load factor 
than the ordinary central station generating plant — it will be 
seen that the average true load factor of the remaining plants 
is somewhere in the vicinity of 28 per cent., which is a fair average 
for central station generating plants of medium size. 

It is not at all surprising to find a large variation in the 
amount of fuel consumed per kilowatt hour, and also in the 



56 ENGINEERING FOR CENTRAL STATIONS 

cost of fuel per ton, in the case of a group of plants which are 
very diversely located as regards facilities for obtaining coal ; 
and which differ widely in their types of generating equipment, 
upon which the consumption of fuel per unit of output so largely 
depends. It will be noted that the cost of fuel ranges from 
$2.14 per ton, as the average cost of a mixture of bituminous 
and anthracite coals, to $5.31 per ton in the case of a small 
plant using bituminous coal. The pounds of coal consumed per 
kilowatt hour show a similarly wide variation, the minimum 
consumption being a trifle under 3 lb. per kilowatt hour in the 
case of a combined engine and turbine plant using a high grade 
of bituminous coal, to over 8£ lb. per kilowatt hour in the case 
of a small plant using a poor grade of bituminous coal and 
having an equipment consisting of simple and condensing engines 
with a number of shaft-driven generators. The cost of fuel per 
kilowatt hour is seen to vary from .36 cents per kilowatt hour in 
the case of a fairly large turbine plant to 1.79 cents per kilowatt 
hour in the case of a very small central station plant with, 
presumably, very inefficient generating equipment. In the aver- 
age central station using bituminous coal it would appear 
that, with a yearly output ranging from some 10 million kilowatt 
hours down to some 5 million kilowatt hours, the average cost 
of fuel per kilowatt hour may ordinarily be taken at about .6 
cents; for yearly outputs below the latter figure the cost will 
usually rise, until, in the case of stations having yearly outputs 
of less than 1,000,000 K. W. hours, the average cost of fuel will 
commonly be in excess of 1 cent, unless such plants are very 
economically designed, or unless the cost of fuel is unusually 
low. For plants of modern design with outputs in the neighbor- 
hood of 20 or 30 million K. W. hours, a unit fuel cost of less than 
A cents may reasonably be expected. 

Coming to the item of labor, almost the same amount of 
variation is seen to exist as in the cost of fuel. It is difficult 
to account for the very considerable variation in the number 
of men employed in different plants of practically the same size 
and having about the same output. The number of kilowatts 
of station capacity per man employed varies from a minimum 
of 90 to a maximum of slightly over 300, the average being 
slightly under 200. It will be seen that for outputs ranging 
from about 2 million up to about 9 million kilowatt hours per 
year, the average cost of plant labor is about .3 cents per K. W. 



KILOWATT HOUR COSTS 57 

hour. For plants of greater output, the cost of labor per unit 
generated may be somewhat below this figure, one plant, in fact, 
with a yearly output of 10 million kilowatt hours, showing a 
unit cost of only .155 cents per K. W. hour, which is an extremely 
low figure for a plant with this output. For plants of smaller 
output the average cost of labor per kilowatt hour naturally 
becomes higher, and the average figure for plants having yearly 
outputs of less than 2 million kilowatt hours would appear to 
be in the neighborhood of .6 or .7 cents per kilowatt hour. 

The cost of repairs shows a very wide variation. This is to 
be expected, when one considers that very different types of 
generating equipments are being compared and that among the 
several plants there are undoubtedly a number of different ways 
of dealing with this item. The cost of water is such an extremely 
variable quantity that the presentation of this item is of little 
value for comparative purposes. The cost of supplies shows 
considerably more uniformity than either of the two items of 
cost just referred to. In two plants, where the generating 
equipment comprises steam turbines only, the cost of supplies 
is seen to be well under .01 cent per kilowatt hour. In those 
plants having steam-engine equipments and with medium 
outputs, the cost of supplies seems to average about .02 cents 
per unit generated, while in the smaller plants, the majority of 
which have belted and shaft-driven equipment, this cost is seen 
to reach .05 cents or more per kilowatt hour. 

For the benefit of those persons who are not particularly 
familiar with the subject of power generation and who may, as 
a consequence, draw erroneous conclusions from a comparison of 
the generating cost figures which appear in the final column of 
the accompanying table with the prices at which electricity is 
commonly sold, the authors desire to place further emphasis upon 
the fact that the figures as given cover the mere cost of generation 
only, and that they make absolutely no allowance for any of the 
fixed or overhead charges that result from the plant investment. 
Moreover when it comes to the question of distributing and 
selling electrical energy, other expenses enter, such as the 
fixed and operating costs of distribution, the cost of management, 
general office expenses, etc., and the total of these items is 
relatively great as compared with the mere cost of generation. 
In addition to this the kilowatt hours produced almost invariably 



58 ENGINEERING FOR CENTRAL STATIONS 

undergo a shrinkage of some 30 or more per cent, during the 
process of distribution. 

No. 1 is a plant which supplies electrical energy to the elec- 
trified portion of a steam railway. The operationg costs as given 
are for the year 1908, at which time the equipment comprised 
three 3-phase, 11,000 volt Westinghouse-P arsons turbo-units of 
5500 K. W. capacity each. The building has space for six 
units of this size, while land has been provided for a total of 
14 such units. Additional units are to be installed as the 
electrification of the system is extended. The boiler plant con- 
sisted of 32 Babcock & Wilcox boilers of about 500 H. P. each, 
operated at a steam pressure of 175 lb. Each boiler is equipped 
with a Roney stoker. Current is transmitted at 11,000 volts 
to substations, where it is changed into direct current of about 
600 volts, at which pressure it is delivered to the third rail. 

No. 2 is the generating plant of an electric high-speed railway 
connecting a large city with a prominent seaside resort about 
75 miles distant. Current is generated by Curtis turbo-alter- 
nators at 6600 volts, 25 cycles, and it is stepped up to 33,000 
volts for transmission to eight substations, where it is changed 
into direct current at 650 volts, at which pressure it is supplied 
to the third rail. The boiler plant consisted of 12 Stirling 
water tube boilers of 358 H. P. each, operated at a steam pressure 
of 175 lb., and with superheat of 125° F. The three sets 
of figures appearing in the "Total Cost" column are for the 
three years 1907, 1908 and 1910 respectively, and they show 
that the total cost of generation has been gradually reduced as the 
load upon this plant has increased. The data in the remaining 
columns ref r to the year 1908. 

No. 3 is a generating plant of modern design which supplies 
electrical energy to four towns in which sub-stations are located. 
A large percentage of the output is sold to electric railways. 
Out of total sales of 15,750,930 K. W. hours for the calendar year 
1908, 15,502,095 were disposed of for railway service. The 
boiler plant consisted of eight Heine boilers of 488 H. P. each 
and four Cahall boilers of 509 H. P. each, making a total of 
5940 H. P. These boilers were operated at a steam pressure 
of 175 lb. The generating equipment consisted of two 1000 
K. W. and two 2000 K. W. Curtis turbo-alternators wound for 
2300 volts. The cost of this generating plant is stated to have 
been as follows: 



KILOWATT HOUR COSTS 59 

Station building $337,273.43 

Steam equipment 268,126.74 

Electrical equipment 187,440. 10 

The total cost of this plant is therefore $792,840.27, or $132 
per kilowatt of rating. The low cost of generation in this plant 
is, or course, due to the modern equipment, to the low cost of 
fuel and to the high load factor under which this plant is 
operated. 

No. 4 is a plant which supplies electrical energy to an inter- 
urban railway that has a total length from end to end of about 
30 miles. The greater part of the line is double track, and the 
total mileage, including several single track branch lines, aggre- 
gates about 75 miles. The car mileage during the year for 
which the operating costs are given was 1,820,985. Current is 
generated in this station at 13,200 volts, at which voltage it is 
transmitted to four rotary converter and step-down transformer 
sub-stations, located along the length of the line. The total 
amount of energy delivered by these sub-stations during the 
year was 8,095,060 K. W. hours, which gives a transmission 
and reduction efficiency of about 80 per cent. The cost of 
600- volt D. C. power as delivered by the sub-stations, was 
approximately 1.045 cent. The generating plant is located 
22 miles from tide water and it is necessary to team coal to 
the storage yard, from which it is wheeled into the boiler room. 
The engines and turbines are operated condensing, a cooling 
tower installation having been provided with motor-driven 
fans. 

The boiler equipment consisted of two 650 H. P. and three 
500 H. P. water tube boilers. The generating equipment con- 
sisted of one 2000 K. W., 13,200 volt, 25 cycle, 3-phase Curtis 
turbine set and two Rice & Sargent engines direct-connected to 
General Electric alternators of 500 and 1000 K. W. rating. The 
steam pressure carried is 150 lb. Jet condensers are used in 
connection with the engine units, which are of the cross-com- 
pound type. The turbine unit is provided with a surface con- 
denser, but this unit is only operated during periods of heavy 
load. 

No. 5 is a central station plant, A to E covering the years 
1905 to 1909 inclusive. During this period the plant underwent 
a considerable increase in capacity and in output. In 1905 the 
generating equipment comprised three Allis compound engines, 



60 ENGINEERING FOR CENTRAL STATIONS 

one Corliss engine, one Ball engine and one Allis-Chalmers engine, 
with an aggregate rating of 4300 H. P. These engines were 
employed for driving a total of 17 dynamos. The boiler plant 
consisted of 10 Roberts horizontal return-tubular boilers and 2 
Babcock & Wilcox water-tube units. By 1909 the horizontal 
return tubular boilers had been replaced by water-tube boilers 
of the Babcock & Wilcox type, while two 1500 K. W. Curtis 
turbo-alternators had been added and the belt-driven generating 
equipment discarded, with the exception of three small power 
generators of 186 K. W. each supplying direct current at 500 
volts. The power sales amounted to a little over 40 per cent. 
of the total energy sales during the year 1909, the power load 
served being one of a highly diversified character. 

No. 6 is a central station plant supplying a community of 
about 40,000 inhabitants. A is for the year 1909 and B for the 
year following. The generating equipment consisted of two 
1500 K. W. Curtis turbine units of the vertical type. The boiler 
plant comprised four water-tube boilers of Babcock & Wilcox 
make, with a total rating of 2100 H. P. This plant is now about 
4 years old, and it replaced an old plant of the belted and shafting 
type which contained engines of relatively low efficiency. It is 
located about 6 miles from the old plant, which was situated in 
the center of the town. The new locality is in close touch with 
an industrial district of large possibilities. The load factor upon 
this plant was considerably higher in the year 1910, largely as a 
result of added motor load, and the cost of generation showed a 
marked reduction over the preceding year. Of the total sales 
for the year 1910, approximately 40 per cent, was disposed of for 
power purposes. 

No. 7 is the plant of a central station which serves a large 
city of the residential type which has a rapidly growing electric 
motor load in its manufacturing section. The total kilowatt 
hours sold during the year 1910 were 6,566,420, of which 3,027,- 
476 were disposed of for power purposes. This plant is located 
upon a river which permits of coal being delivered at the station 
in barges. The boiler plant consists of eight boilers of 400 H. P. 
each, operated at 160 lb. steam pressure. The generating plant 
consists of three main generating units, each consisting of an 
alternator direct-connected to a vertical cross-compound con- 
densing engine. In addtion, two 250 K. W. motor-generator 
sets are in use for supplying a certain amount of direct-current 



KILOWATT HOUR COSTS 61 

motor load. It is stated that additional capacity in this station 
is to be provided by the installation of low pressure turbine 
equipment. 

No. 8 is a central station plant, A and B representing the costs 
of operation for the years 1909 and 1910 respectively. The 
generating plant consisted of one 1500 K. W. Curtis turbo-alter- 
nator, together with three engine-driven alternators with a 
total rating of 2250 K. W.; also six small belt-driven arc lighting 
and railway-type direct current generators. The boiler plant 
consisted of 12 horizontal return tubular boilers with an aggre- 
gate nominal rating of 3000 H. P. The company which operates 
this plant has undertaken an energetic campaign for power 
business, which is shown by an improvement in the load factor 
and by the lowered cost of operation for the latter of the 2 
years which are here compared. The power sales in 1910 were 
almost double what they were during the year preceding. 

No. 9 is a central station plant, and the operating costs as 
given are for the year 1908. The boiler plant comprised six 
Babcock & Wilcox boilers of 400 H. P. each, operated at a steam 
pressure of 160 lb. The generating equipment consisted of two 
750 H. P., one 2250 H. P. and one 3000 H. P. vertical cross-com- 
pound condensing engines of Mcintosh & Seymour make. 
These engines were direct-connected to two 600 K. W., one 1500 
K. W. and one 2000 K. W. alternators, while there were in 
addition two 125 K. W. 500 volt direct-current generators, 
which were driven by a direct-connected alternating current 
motor. The 2000 K. W. unit was installed in the year 1908. 

The operating costs of this plant for 3 years prior to 1908 
were 1.12 cents, 1.12 cents and 1.05 cents. The increased cost of 
generation in 1908 was due almost entirely to an increase in the 
cost of coal, which had advanced from $3.35 per ton in 1905 to 
$4.40 in 1908. 

No. 10 is the generating plant of a central station which serves 
a population of about 35,000. A is for the year 1909, while B 
is for the year following. In 1909 the boiler plant consisted of 
four water tube boilers with an aggregated rating of 1910 H. P. 
The generating plant consisted of three compound condensing 
engines of 2000 H. P. combined rating and a horizontal steam 
turbine of 1500 K. W. capacity. The cost of generation for 
these 2 years remained practically the same. The motor 
Bales for the year 1910 were only 30 per cent, of the total sales, 



62 ENGINEERING FOR CENTRAL STATIONS 

and it is probable that the existing operating costs will be some- 
what reduced as the amount of motor load is increased. 

No. 11 is a central station plant which passed through a gradual 
process of evolution during the 4 years preceding 1908, to 
which year the figures in the accompanying table relate. From 
an almost entirely belted installation, this plant has been changed 
into one consisting of direct-connected compound condensing 
engine units, together with one turbo-alternator, while water- 
tube boilers have replaced the original installation of horizontal 
return tubular boilers. The cost of power per K. W. hour has 
been reduced from 1.56 cents in 1904 to 1.24 cents in 1908. While 
this reduction is not extremely large, it has been a steady im- 
provement, and the saving will be more marked as the load upon 
the plant increases. The boiler plant in 1908 consisted of 12 
water-tube boilers of 250 H. P. each, operated under a steam 
pressure of 140 lb. The generating plant consisted of four 
reciprocating compound condensing engines, aggregating 3900 
H. P., and a Curtis turbo- alternator of 1500 K. W. rating. 

No. 12 is a central station generating plant. The total sales 
for the year 1910 were 3,822,311 K. W. hours, of which 961,207 
were sold for motor uses. This station is favored with tide water 
delivery of coal. The boiler plant consists of six water tube 
boilers rated at 350 H. P. each. The generating equipment con- 
sists of Curtis turbines of the vertical type, two being of 500 
K. W. and one of 1500 K. W. capacity. With an increase in 
the sales of electrical energy for power purposes, it is reasonable 
to expect that even the present low cost of generation in this 
plant will be somewhat lessened. 

No. 13 is the plant of a central station which serves a commu- 
nity of a little over 40,000 inhabitants. A and B are for the 
years 1907 and 1908 respectively. The generating plant con- 
sisted of one 900 and one 1500 H. P. Mcintosh & Seymour 
engine and one 500 H. P. Providence engine. Both belted and 
direct-connected generators were in use, the total capacity aggre- 
gating 2500 K. W. The boiler plant consisted of 11 boilers 
having an aggregated rating of 1350 H. P. 

No. 14 is a central station plant, and A, B and C represent the 
years 1908, 1909 and 1910 respectively. In 1908 the boiler 
equipment consisted of five Stirling boilers of 258 H. P. each, 
operating at a steam pressure of 150 lb. The generating units 
comprised one 600 H. P., one 900 H. P. and one 1500 H. P. 



KILOWATT HOUR COSTS 63 

Mcintosh & Seymour engine, direct-connected to a 400 K. W., 
a 600 K. W. and a 1000 K. W. General Electric alternator 
respectively. For the 3 years prior to 1908, the operating costs 
of this plant were 1.4 cents, 1.07 cents and 1.42 cents. After 
the year 1908 it will be seen that the operating costs were materi- 
ally reduced. This largely resulted from a considerable increase 
in the yearly output, due to a considerably greater amount of 
power business. In the year 1909 the company sold more than 
one-half of its output for electric motor service, which increased 
to approximately 60 per cent, in the year 1910. The total popu- 
lation served by this plant in 1910 was a little less than 40,000. 

No. 15 is the plant of an electric railway in the middle west. 
It is a remodelled installation, the present turbo-generators 
having replaced reciprocating direct-connected engine units. 
As a result of these improvements and of an increased output, 
the generating cost has been reduced from 1.1 cents per kilowatt 
hour in 1906 to .72 cent per kilowatt hour in 1908. It will be 
observed that the latter figure is extremely low for a plant of this 
size, which is probably due to the modern generating equipment 
and to the high load factor afforded by the railway load. 

No. 16 is a central station plant serving a population of 
about 40,000. B and A are for the years 1908 and 1909 respec- 
tively. In the latter year the generating equipment consisted 
of one 400 H. P. Harris horizontal cross-compound condensing 
engine belt-connected to a 300 K. W. alternator and two West- 
inghouse-Parsons turbo-alternators of 1000 K. W. rating each. 
The boiler plant consisted of four Cunningham boilers of 150 
H. P. rating, one Stirling boiler of 660 H. P. rating and two 
Babcock & Wilcox boilers of 650 H. P. rating, the three last 
named boilers being operated at 160 lb. pressure, and two being 
fitted with Roney stokers. The operating costs of this station 
are seen to be quite low for a station of this capacity. 

No. 17 is a central station plant, A and B representing the 
years 1909 and 1910 respectively. This plant disposes of a large 
part of its output to an electric railway, about 90 per cent of the 
total output being so utilized in the year 1910. In 1909 the 
generating equipment consisted of three compound engines 
direct-connected to General Electric 500 volt direct-current 
generators of 850, 525 and 100 K. W. capacity respectively; also 
two Armington & Sims engines driving six arc light dynamos, 
four alternators with a total capacity of 330 K. W. and two 500 



64 ENGINEERING FOR CENTRAL STATIONS 

volt direct-current generators of 100 K. W. each. The boiler 
plant consisted of nine 150 H. P. Cunningham boilers and one 
125 H. P. Dobbins boiler. In 1910 the generating capacity was 
slightly increased, the total being given as 2435 K. W. 

No. 18 is a central station plant, although a very large part 
of the output is sold to an electric railway. The figures as given 
in the accompanying table are for the year 1908. This plant has 
experienced little growth in output during a 4-year period ending 
with 1908, and this fact, taken in conjunction with a gradual 
rise in the cost of fuel during this period and a falling off in the 
fuel economy of the plant due to a gradual depreciation of its 
somewhat antiquated equipment, has resulted in an increase in 
the cost of generation over the period mentioned. In 1905 the 
total output amounted to 4,211,088 K. W. hours, of which the 
total sales were 4,193,369. Of the latter amount, 3,649,145, 
or nearly 90 per cent., were sold for railway purposes. By 1908 
the power sales had increased by only a very slight extent and 
amounted to 3,672,000 K. W. hours. The costs of generation 
for the 3 years prior to 1908 were as follows: 1905, 1.07 cents 
per K. W. hour; 1906, 1.07 cents per K. W. hour; 1907, 1.35 
cents per K. W. hour. 

No change was made in the equipment during this 4-year 
period. The boiler plant consisted of one 125 H. P. and nine 
150 H. P. shell-type boilers, operated at a steam pressure of 
110 lb. The plant contained six engines, comprising four differ- 
ent makes, and all but one of the compound condensing type. 
These engines ranged in size from 100 H. P. to 1250 H. P., and 
only two were direct-connected to generators. The plant 
contained 15 generators, of which 13 were belt-driven. 

No. 19 is a central station plant which serves a population of 
about 30,000. During the year ending June 30, 1908, the total 
sales were 2,572,978 K. W. hours. The boiler plant consisted 
of four 350 H. P. Stirling boilers operated at 175 lb. steam pres- 
sure; five Robinson boilers of 125 H. P. each, operated at 115 lb. 
pressure, three 125 H. P. Dillon boilers operated at 115 lb. 
pressure. v The engine plant consisted of one Wetherill 600 
H. P. engine, one Armington & Sims 300 H. P. engine and two 
Westinghouse 500 K. W. turbo-alternators. 

No. 20 is the plant of a central station serving a town of about 
16,000 inhabitants. A, B and C are for the years 1908, 1909 
and 1910 respectively. The generating equipment, which 



KILOWATT HOUR COSTS 65 

remained unchanged during this period, consisted of two 750 
K. W. horizontal Curtis turbo-alternators wound for three- 
phase, 2300 volt, 60 cycle current, one 100 K. W. alternator 
belted to an Armington & Sims simple engine, one 250 K. W. 
alternator driven by a Mcintosh & Seymour horizontal, tandem- 
compound, condensing engine and one 500 K. W. generator 
direct-connected to a Lane & Bodley cross-compound engine. 
The boiler plant comprised six water-tube boilers, aggregating 
1349 H. P., operated at a steam pressure of about 140 lb. While 
the generating equipment remained the same over the period 
mentioned, minor changes in the plant were made which tended 
toward improvement in the generating efficiency. This plant 
has experienced a considerable improvement in load factor due 
to an increase in the amount of current sold for power purposes. 
During the year 1910 about 66 per cent, of the total energy sales 
were disposed of to motor users. 

No. 21 is a central station plant and is under the same general 
management as plant No. 10 and the two plants are so located 
with respect to one another that they may be tied together. The 
two plants are usually so operated that the smaller one is shut 
down during such times as it cannot be efficiently loaded. 
During such periods electrical energy is purchased from the 
plant referred to and from another nearby central station under 
separate management. The boiler plant consists of four water 
tube boilers with a total rating of 1208 H. P. and operated at a 
steam pressure of 135 lb. The generating equipment consists 
of a Westinghouse-Parsons turbine of 500 K. W. rating and two 
alternators direct-connected to Rice & Sargent horizontal cross- 
compound engines. 1,538,793 K. W. hours were sold during the 
year 1910, of which only 111,596 were disposed of for the opera- 
tion of motors. The power load is thus seen to be of insignificant 
amount, but the method of operating the equipment in conjunc- 
tion with the two neighboring plants, as above outlined, results 
in an unusually low operating cost for a plant of this size. 

No. 22 is a central station plant located in a community of 
about 30,000 inhabitants. A and B are for the years 1908 and 
1909 respectively. The generating plant consisted of three 
General Electric alternators of 150 K. W., 300 K. W. and 800 
K. W. capacity direct-connected to one simple and two compound 
engines respectively. The boiler plant comprised four Babcock 
& Wilcox boilers with a total rating of 1000 H. P. 

5 



66 ENGINEERING FOR CENTRAL STATIONS 

No. 23 is a central station plant, A to D covering the years 

1906 to 1909 inclusive. In the former year the generating 
equipment consisted of one Greene cross-compound condensing 
engine rated at 175 H. P. and one similar engine rated at 350 
H. P. The electrical equipment comprised three 150 K. W. 
belted alternators and three 44 K. W. Brush arc machines. In 

1907 a 500 K. W. turbine unit was added. The boiler plant 
consisted of four Babcock & Wilcox water-tube boilers operated 
at a steam pressure of 120 lb., the aggregated rating being 678 
H. P. The costs of operation — with the exception of the year 
1909 — show a steady increase, although the cost of coal remained 
practically unchanged. This increased operating cost would 
appear to be due to a falling off in the general plant efficiency, due 
to the continued operation of old and relatively inefficient 
generating equipment. 

No. 24 supplies direct current at 550 volts to a street railway 
located in a city with a population of about 20,000. The 
electric railway connects this city with a small town about 3 
miles distant, and it also extends to a lake situated at about the 
same distance in another direction, where a pleasure park is 
located, which provides a considerable amount of additional 
traffic during the summer months. There are about 15 miles 
of single track line, and, except during the summer when the 
park is open, eight or nine cars are normally in operation. The 
total car mileage for the year 1910 was a little over 600,000, and 
the cost of power per car mile was 2.87 cents. The plant oper- 
ating costs were approximately 18 per cent, of the total operating 
expenses of the road, exclusive of interest, depreciation, insurance 
and taxes. 

The generating plant is located about a mile from the center 
of the city near the banks of a small stream from which condens- 
ing water is obtained. A spur from a steam railroad makes 
possible the delivery of coal in car-load lots, the coal being dumped 
directly from the cars into a storage bin located adjacent to the 
boiler room. This plant was remodelled in 1909, up to which 
time power was generated by means of high-speed engines with 
belt-connected generators. When the present generating units 
were installed, the old fire tube boilers were replaced with boilers 
of the water-tube type. The plant at present consists of one 
300 K. W. General Electric generator direct-connected to a 450 
H. P. Watts-Campbell tandem compound engine, which is pro- 



KILOWATT HOUR COSTS 67 

vided with a Worthington condenser, and one 500 K. W. Curtis 
horizontal turbo-generator, provided with an Alberger centrif- 
ugal condenser. The boiler plant consists of two 300 H. P. 
Rust water-tube boilers. 

No. 25 is a central station plant which serves a population of 
a little over 30,000. During the year ending June 30, 1908, the 
total sales amounted to 837,640 K. W. hours. The boiler plant 
consisted of four 125 H. P. Roberts boilers operated at 120 lb. 
steam pressure. The generating equipment consisted of one 
500 K. W. Curtis turbine, one 400 H. P. Allis-Corliss engine and 
one 250 H. P. Mcintosh & Seymour engine. The generator 
equipment comprised three belted and one direct-connected 
alternators. 

No. 26 is the plant of a small central station, A, B and C 
representing the years 1906, 1907, and 1908 respectively. The 
capacity of the plant underwent an increase during 1907 by the 
addition of a Mcintosh & Seymour engine unit of 250 H. P. 
In 1906 the generating equipment consisted of one Armington 
& Sims high-speed compound engine of 250 H. P., one Mcintosh 
& Seymour compound engine of 250 H. P. and one Ball & Wood 
simple engine of 211 H. P. The generating equipment consisted 
of one 175 K. W. Bullock alternator and two General Electric 
alternators of 200 K. W. each. Viewing the operation of this 
station over the 3-year period, it would appear that this 
plant has been handicapped by a rise in the cost of coal, but that 
an increase in the power load has permitted of a somewhat 
more economical operation of the plant. It will be seen that the 
cost of labor per unit generated for this plant is unusually high. 

No. 27 is a central station plant, the cost of operation being 
given for the year 1908. The steam generating equipment 
consisted of three 150 H. P. and one 125 H. P. horizontal re- 
turn tubular boilers, operating at a steam pressure of 125 lb. The 
plant contained five engines with a total of 12 generators. The 
engines comprised one Buckeye compound condensing outfit 
rated at 250 H. P.; one Armington & Sims engine of 100 H. P. 
rating; one Buckeye engine of 300 H. P., and two Dick & Church 
engines of 175 H. P. each. The amount of power load supplied 
by this plant was extremely small, and it will be observed that 
the demand upon the plant in relation to its capacity was 
unusually low, the average load being only 11 per cent, of the 
generator rating. 



68 



ENGINEERING FOR CENTRAL STATIONS 



No. 28 is the generating plant of a small central station which 
was able to progressively lower its operating costs for the 4 years 
ending with the year 1908. The following table gives a summary 
of the operating data of this plant for the 4 years, 1905 to 
1908 inclusive. 





1905 


1906 


1907 


1908 


Tons of coal used 


1,570 
4.05 
420,520 

1.52 
.89 
.37 

2.78 


1,665 

4.07 
484,119 

1.41 
.77 
.39 

2.57 


1,845 

4.31 
636,486 

1.25 
.605 
.285 

2.14 


1,629 

4.15 

730,458 

.925 

.685 

.190 

1.80 


Average cost per ton 

K. W. hours generated 

Fuel 

Labor 

Miscellaneous 

Total 



The generating equipment in this plant remained practically 
unchanged during these 4 years. The reduction in the cost of 
generation was almost directly due to an increased output, 
which resulted largely from an increase in the sales of electrical 
energy for power purposes. 

The boiler plant consisted of one Strothers & Wells 150 H. P. 
boiler and two Babcock & Wilcox boilers of 200 H. P. each. 
The engine equipment consisted of one tandem compound con- 
densing unit and two cross-compound condensing units, all of 
Mcintosh & Seymour make. The ratings of these engines at 
normal loads were 250, 125 and 250 H. P. respectively. The total 
generator capacity in 1908, comprising both A. C. and D. C. 
machines, was 630 K. W. 



CHAPTER VII 
CENTRAL STATION LOAD FACTORS » 

The term "load factor/' as used in connection with the genera- 
tion of electrical energy, has been employed to convey a number 
of different meanings. One conception of load factor — and 
probably the most common one — defines it as the average load 
upon the station throughout the year expressed as a percentage 
of the maximum observed load upon the station during the same 
period. Sometimes the term "plant load factor" is used to 
express the ratio of the average load upon the generators during 
the year to the aggregate rated generating capacity, including 
spare units; while the term "station load factor" is taken to 
mean the ratio of the average load on the station feeders during 
the year to the maximum observed load upon these feeders. 
Then again, load factor is sometimes given quite a different 
meaning, and is denned as being the ratio of the average load, 
as represented by the electrical energy actually sold to the con- 
sumers, to the maximum load supplied to the feeders at the 
station, expressed as a percentage. As thus defined, the load 
factor could never reach 100 per cent, even if each consumer were 
to use his maximum for 24 hours per day throughout the year, for 
the reason that the average load, which would be equivalent to 
the total kilowatt hours sold during the year divided by 8760, 
would always be less than the load upon the feeders on account 
of the losses occurring in transmission and distribution. 

The load factor of a generating plant — not necessarily the 
plant of a central station — is frequently based upon a time 
interval of 24 hours, the load factor over a given period being 
denned as the ratio of the average 24-hour load upon the gener- 
ators to the rated capacity of the generating units, expressed in 
the form of a percentage; the term "true load factor" being then 
used to express the ratio of the average 24-hour load to the maxi- 
mum load, likewise in the form of a percentage. An additional 

1 This chapter first appeared as an article in the Electrical World, Vol. 59, 
p. 258. 

69 



70 ENGINEERING FOR CENTRAL STATIONS 

term, designated as "loading factor," is sometimes employed to 
express the ratio of the average load carried by a single generator 
or by several generators, throughout a period of 24 hours, to the 
continuous rated capacity of such generator or generators, this 
also being usually expressed in the form of a percentage. 

The definition of load factor first given, which is the one that 
is most generally used, is susceptible of two slightly different 
interpretations, but the differences which they involve are 
usually of very small consequence. The average load on a 
station may be taken to mean the average load upon the gener- 
ators or the average load upon the feeders, while the maximum 
load may, in a similar manner, be considered as referring to the 
maximum load upon the generators or to the maximum load 
upon the feeders. The difference between these two sets of 
measurements represents, of course, the amount of electrical 
energy used within the station itself, plus any losses that may 
occur between the two points of measurement. As the amount 
of electrical energy that is used within the station is usually an 
exceedingly small percentage of the amount sent out over the 
feeders, little confusion is likely to result from the very slight 
amount of uncertainty that is involved in the use of this definition 
of load factor. 

The accompanying table gives the load factors of a number of 
central stations located in this country, the majority of the figures 
being for the year 1910. The load factor as given is the ratio of 
the total K. W. hour output for the year to the maximum demand 
in K. W. multiplied by 8760 hours, expressed as a percentage, 
this being, of course, precisely the same quantity as the ratio of 
the average load during the year to the maximum load, expressed 
as a percentage. 

Curve A in Fig. 13 shows the increase in load factor on the 
low-tension direct-current network of a large central station 
from 1892 to 1910, inclusive — a period of almost 20 years. It 
will be seen that the load factor has increased during this period 
from 20 per cent, to approximately 30 per cent., a figure which 
still leaves much to be desired. As this increase in load factor 
has almost entirely resulted from an increase in the use of elec- 
trical energy for purposes other than lighting, it is of interest to 
observe the increase during the same period of the percentage 
relation which the connected load in motors, heating devices, 
storage batteries, etc., bears to the total load connected to the 



CENTRAL STATION LOAD FACTORS 



71 



TABLE SHOWING YEARLY OUTPUT IN KILOWATT HOURS, 
MAXIMUM DEMAND IN KILOWATTS AND LOAD FACTOR, 
EXPRESSED AS A PERCENTAGE, FOR A NUMBER OF 
CENTRAL STATIONS 





Maximum 




Yearly output in kilowatt 


demand in 


Load factor in 


hours 


kilowatts 


per cent. 


A 


878,140 


487 


20.5 


B 


1,481,000 


555 


30.5 


C 


2,625,937 


1,550 


19.3 


D 


3,238,766 


1,700 


21.7 


E 


3,288,623 


1,210 


31.0 . 


F 


3,721,153 


1,675 


25.4 


G 


4,408,965 


1,950 


25.8 


H 


4,462,550 


1,625 


31.3 


I 


4,715,000 


1,650 


32.6 


J 


5,858,255 


2,510 


26.6 


K 


5,960,000 


2,760 


24.6 


L 


8,789,195 


3,175 


31.6 


M 


8,800,828 


3,350 


30.0 


N 


8,904,300 


2,900 


35.1 





10,185,832 


4,330 


26.9 


P 


11,100,000 


4,700 


26.9 


Q 


15,540,035 


5,270 


33.7 


R 


16,500,000 


9,800 


19.2 


S 


16,930,345 


6,000 


32.2 


T 


19,037,529 


7,725 


28.2 


U 


22,179,000 


10,348 


24.5 


V 


23,053,128 


7,700 


34.2 


W 


25,297,757 


12,325 


23.4 


X 


32,773,730 


10,260 


36.5 
Average 28.0 



system. This is shown by curve B. The actual increase has 
doubtless been somewhat greater than is disclosed by this curve, 
for the reason that many electrical heating appliances and 
similar devices have undoubtedly been connected during the past 
few years without any opportunity being afforded the central 
station of placing them upon its records. It is also reasonable 
to assume that there have been many cases where tungsten or 
other of the higher efficiency lamps have been substituted for 



72 



ENGINEERING FOR CENTRAL STATIONS 



carbon lamps of higher wattage without the central station being- 
able to record such substitution. However, as the records of 
this central station have been very carefully kept, it may be 
assumed that curve B very closely represents the actual condi- 
tions as regards connected load over the period selected. It is of 
interest to note that the portion of the connected load other than 
lighting has increased from approximately 26 per cent, of the 
total connected load in 1892 to nearly 50 per cent, in 1910. 



50 












































































































































































































































































































! 






































" Cu 


rv 


e j 


b 












































/ 


















































40 






















/ 








































































S 








































































/ 








































































/ 


/ 






























































30 










/ 






































































/ 




















































/ 
































































































































xc 


je 


Z* 








































































































20 
















































































































































































































































































































































Curved- Load Factor in Per Cent 
Curve B- Ratio of Power, Heating, 
and Storage Battery. 
Load to Total Connected 
Load in Per Cent. 


- 


10 



























































































































































































































































































































1892 1893 1894 1895 1896 1897 1898 1899 1900 1901 1902 1903 1904 1905 190G 1907 1908 1909 1910 

Fig. 13. 



The introduction of the higher efficiency lamps should naturally 
tend, provided other conditions remained the same, to reduce the 
percentage which the connected lighting load bears to the total 
connected load, and, as a consequence, some betterment in the 
load factor should result. The adoption of these higher efficiency 
lamps, however, has disclosed the fact that other factors now 
enter to modify the conditions that existed prior to the advent of 
these lamps. For instance, up to the present time, many central 
stations have experienced little or no loss in their rate of increase 
in connected load due to the introduction of these lamps, partly 
as a result of being able to secure enough additional business — 
due to the lessened cost of electric light — to offset the reduction 
in the load that might otherwise have resulted, and also partly 



CENTRAL STATION LOAD FACTORS 73 

due to the fact that the higher efficiency lamps have, in some 
degree, resulted in an advanced standard of lighting, the con- 
sumer taking a portion of the gain due to the improved efficiency 
in the form of more illumination, rather than taking it all in the 
form of a reduction in the connected load and in the amount of 
electrical energy consumed. Under such conditions as these, the 
introduction of the higher efficiency lamps has little or no effect 
upon the ratio which the connected lighting load bears to the 
total connected load. Curve B would seem to show that, in the 
case of the central station under consideration, the effects of the 
introduction of the higher efficiency lamps have been fully offset 
by one, or by a combination of both, of the factors above men- 
tioned. Whether such a condition will continue depends upon 
whether the increase in the number of lighting customers is 
sufficiently great to offset the lower connected lighting installa- 
tion per customer. If the number of new users is not sufficiently 
great to overcome the reduction in the lighting installations of 
existing customers, curve B will naturally tend to rise more 
rapidly than it would if governed solely by the gradual increase 
in the percentage relation which that portion of the connected 
load other than lighting bears to the total connected load. 

Aside from this question, however, it would appear that the 
higher efficiency lamps should have an appreciable effect upon 
the load factors of central stations. The lessened cost of electric 
light that has resulted from the introduction of these lamps is 
almost certain to bring about a more extended use of electric 
light; that is, not alone an increase in the number of users — a 
result that is already apparent — but an increase in the number of 
hours of daily use of the average lighting installation. 

A central station which has secured a considerable amount of 
railway load, reports a load factor of slightly over 41 per cent, 
for the year 1910. The acquisition of railway load by a central 
station will almost invariably result in an improvement in the 
load factor. The load factor of the average central station is 
probably slightly below 30 per cent., while the load factor of the 
average electric railway is usually some 40 per cent, or over. 
The railway "peak" rarely, if ever, coincides with the central 
station lighting "peak," as a result of which the load factor of 
the central station is benefited by the railway load to a greater 
extent than it would be by the acquisition of a load of equally 



74 



ENGINEERING FOR CENTRAL STATIONS 



high load factor, but with a maximum demand coincident with 
that of the central station. 

By means of Fig. 14 it is possible to compare the variations in 
the demand for transportation throughout the 24 hours of a 
working day, under the conditions existing in New York City, 
with the variations in demand for electrical energy, as represented 
by the output of the central station over a characteristic 24-hour 
period taken in the month of December at about the time of the 
maximum yearly load. The transportation load curve, which is 
shown by heavy lines, is based upon observations made by the 



ioo 4-£U\ 


-i4A 


J i^ 


80 t £\X 


t tXt 


-tv -T u 


f\ 7- 1 5-\ 




60 it -J i t ^ 


t ju-~ - r ^ X S 


2 vl^-^ X v 


40 4- ^^Jst y a X 


7- \- V 


-i -4 \ ^ 


7 J_ • ^-^ 


in \ / / \ 


20 ^=^_ i-- / i 


V ^ h it 


^ z 


->^ y 



12 



A.M. 



10 12 2 

Fig. 14. 



6 
P.M. 



10 12 



Public Service Commission, and it shows the volume of the traffic 
upon the surface lines in New York City at half-hourly intervals 
throughout the 24 hours of an ordinary business day, the total 
traffic existing at the time of the observed "peak" being taken 
as 100 per cent. The half hourly loads upon the central station 
are likewise expressed in percentages of the maximum load 
throughout the 24 hours. It will be observed that the trans- 
portation "peak" occurs at 6:00 p. m., which is 1 hour later 
than the time of the central station "peak." The 24-hour 
transportation load factor is found to be approximately 38 per 
cent., but the yearly transportation load factor would be prac- 
tically the same, inasmuch as the transportation requirements — 
except in so far as they are affected by the natural growth in 
traffic — remain practically constant throughout the year. The 



CENTRAL STATION LOAD FACTORS 75 

central station load factor for the day shown was 43.7 per cent., 
but the yearly load factor, based upon the maximum yearly 
load, was a trifle under 30 per cent. A generating station supply- 
ing electrical energy for these transportation requirements 
would have a load factor considerably higher than that shown by 
the transportation load curve, for the reason that the power 
demands of an electric railway do not vary to such an extent as 
does the volume of traffic that is being handled, due to the fact 
that the bulk of the power is required for moving the cars them- 
selves, and is therefore independent of the amount of live load 
that is being carried, and to the further fact that the number of 
cars in service is not varied in direct proportion to the variations 
in the total passenger traffic. 

However, this matter of the desirability of securing railway 
load is now very generally recognized by central station mana- 
gers. The argument that a manufacturer should devote his 
undivided attention to the manufacture of his final product and 
not dissipate his energies by undertaking the production of the 
various elements — of which power is usually an important one — 
that enter into the composition of this product, applies, with 
almost equal force, to those who are engaged in the business of 
supplying transportation. Central stations should control the 
entire field of power generation within their respective territories, 
and such an achievement will undoubtedly be brought about 
eventually when the advantages that" result from specialization 
and concentration in this field shall have been fully realized. 

However, if central stations are to obtain higher load factors 
than those afforded by the entire light and power requirements 
of the communities which they serve, special kinds of load must 
be secured to fill in those low portions of the daily and yearly 
load curves that will otherwise continue to exist as a result of 
the unavoidable variations in the demand for electrical energy 
throughout each 24 hours and throughout the year. It is 
unnecessary to say that no one kind of load has as yet been found 
that fulfills all of the requirements of this "filling-in" process, 
although several have been tried that meet some of the require- 
ments in a more or less satisfactory manner. Probably the 
most successful of these, up to the present time, is to be found 
in the manufacture of ice in conjunction with the generation of 
electrical energy. 

This question of finding a satisfactory form of "off-peak" 



76 ENGINEERING FOR CENTRAL STATIONS 

load is of tremendous importance to the central station industry 
and it well warrants the vast amount of thought that is being- 
expended upon it by those engaged in central station work. To 
give some idea of the economic loss that is now occasioned by 
the poor utilization of the electrical generating equipment in the 
central stations of this country, it is only necessary to refer to the 
report of the Bureau of the Census for the years 1902 and 1907. 
In 1902 the total generating equipment of the central stations of 
this country was stated as being 1,212,235 K. W. and the yearly 
output in kilowatt hours 2,507,051,115. These figures show 
that this total generating equipment was utilized at its rated 
capacity only during a little over 23 per cent, of the entire year. 
In 1909, the generating equipment had increased to 2,709,225 
K. W., while the kilowatt hour output had increased to 
5,862,276,737. These latter figures show that the entire rated 
generating capacity was in use during only slightly over 24 per 
cent, of the entire year. It was recently stated that 97 per cent, 
of the total kilowatt hours generated by a large central station 
was produced by 50 per cent, of the total generating apparatus 
installed, the other 3 per cent, being generated by the remaining 
50 per cent, of the generating capacity. As a result of this, 
50 per cent, of the generating equipment is being operated at 
a little under 50 per cent, load factor, while the yearly load 
factor of the balance of the generating equipment is only some 
5 or 6 per cent. 



CHAPTER VIII 

ELECTRICITY IN THE MODERN DEPARTMENT STORE 

The diversity of uses to which electricity is applied in the 
modern department store is almost comparable with the diversity 
of the lines of merchandise handled by a store of this character. 
Besides its use for lighting purposes and for the operation of 
elevators, electricity is usually employed in this class of buildings 
for operating ventilating fans, for pumping water, for running 
sewing machines, for conveying packages and for operating a 
large number of small motors that are applied to a great variety 
of uses. It is frequently employed for operating the cash-carrier 
system and occasionally for operating the compressor and the 
brine-circulating pump of the refrigerating plant, which now 
usually forms part of the mechanical equipment of the modern 
department store. A list of the various motors in a certain 
representative department store is given below, and it clearly 
shows the diversity of the uses to which the electric motor is 
applied in a store of this character. 

ELECTRIC MOTOR EQUIPMENT OF A LARGE DEPARTMENT STORE 



Forty-three 115 ampere elevators. 

Two 75-ampere elevators. 

One 1-H. P. mangle. 

One 1/2-H. P. mangle. 

One 10-H. P. drive. 

One 2-H. P. drive. 

One 1-H. P. laundry machine. 

One 17 1/2-H. P. fan. 

Three 16-H. P. fans. 

Two 13-H. P. fans. 

One 12-H. P. fan. 

One 11-H. P. fan. 

Cne 10-H. P. fan. 

Two 8-H. P. fans. 

One 2 1/2-H. P. fan. 

One 1-H. P. exhaust fan. 

Five 6-H. P. dumb-waiters. 

Fifty-one 1/7-H. P. sewing machines. 

Eight 1/8-H. P. sewing machines. 

One 1-H. P. carpet sewing machine. 

One 1-H. P. buffer. 

One 3/4-H. P. buffer. 

One 1/2-H. P. blower. 

One 1/4-H. P. lathe. 

One 1/4-H. P. drill. 



Two 2-H. P. dish washers. 

Two 10-H. P. compressors. 

One 7 1/2-H. P. compressor. 

Five 1/15-H. P. hair dryers. 

Two 2-H. P. ice cream freezers. 

One 2-H. P. ice chopper. 

One 1/4-H. P. carbonator. 

Five 3-H. P. air washers. 

Four 2-H. P. air washers. 

One 3-H. P. saw. 

Two 5-H. P. sump pumps. 

One 20-H. P. pump. 

Two 10-H. P. pumps. 

One 2-H. P. pump. 

One 50-H. P. fire pump. 

One 15-H. P. ammonia pump. 

One 1-H. P. emery wheel. 

One 5-H. P. paper baler. 

One 3 1/2-H. P. package conveyor. 

One 2 1/4-H. P. package conveyor. 

One 1 1/4-H. P. package conveyor. 

Two 3/4-H. P. package conveyors. 

Five 1/2-H. P. package conveyors. 

Total number of motors 177 

Total horse-power of motors. . 1728 



77 



78 ENGINEERING FOR CENTRAL STATIONS 

Entirely aside from the question of the relative cost of securing 
an adequate supply of electrical energy for its manifold needs, a 
store of this character should use central station service rather 
than depend upon a private generating plant located upon the 
premises, for the reason that any interruption in the supply of 
electrical energy is liable to lead to very serious consequences and 
is almost certain to result, even under the most favorable cir- 
cumstances, in a large financial loss. It does not require a great 
deal of imagination to picture the situation that would arise were 
the lights in a department store, crowded with women and 
children, to be suddenly extinguished, under such conditions of 
outside darkness as are present in the late afternoons of mid- 
winter. Even were a panic avoided by the quick restoration of 
the lights — which might be accomplished were an emergency 
connection with the central station available — experience has 
shown that the financial loss resulting from the thefts that occur 
during even a very short period of darkness is a sufficiently 
serious matter from the owner's point of view. With the number 
of connections usually provided for this class of buildings by the 
central stations of our large cities, the possibility of an interrup- 
tion in the central station service is now too remote to warrant even 
the slightest consideration — which certainly cannot be said of the 
supply from a private generating plant, no matter how well 
designed and how carefully operated such a plant may be. The 
cost of electrical energy is usually such a small percentage of the 
total operating costs of the average department store that the 
owners of these stores are quite naturally loath to sacrifice 
reliability of service for an estimated saving, that, at most, would 
amount to an extremely small percentage of the total cost of 
operation. The word "estimated" in the foregoing sentence has 
been used advisedly, as it is a well-known fact that the estimated 
savings of a great many private generating plants are never 
realized under conditions of actual operation. 

So much for the source from which the supply of electrical 
energy is to be obtained. We will now confine ourselves to the 
uses to which electricity is applied in modern department stores 
and to an examination of certain data relating to such uses. In 
doing this, we will first turn our attention to the subject of 
lighting. 

Prior to the introduction of the higher efficiency incandescent 
lamps — such as the tungsten and the tantalum — the general 



ELECTRICITY IN DEPARTMENT STORES 79 

lighting of department stores was accomplished almost exclu- 
sively by means of arc lamps. This type of lamp is still very 
largely used for this class of lighting, although there have recently 
been some notable instances where the tungsten lamp has been 
employed with extremely satisfactory results. The main floors 
of department stores are generally divided into bays, each bay 
usually having an area of some 400 to 600 sq. ft. The custom 
has been to install an arc lamp in the center of each of these bays, 
thereby making the watts per square foot range from about 1 to 
1.5. The resulting average illumination upon the plane of the 
counters probably ranges for this class of lighting from slightly 
under 2 to something over 3 foot-candles. A large department 
store recently erected, in which tungsten lamps are used almost 
exclusively for lighting, is probably the best lighted — both as 
regards quantity and quality of light — of any existing store of 
this character. The main floor is lighted by means of 250 watt 
tungsten lamps placed inside of 14-in. ground glass balls. These 
lights are supported at a distance of 16 ft. from the floor, the 
height of the ceiling being 20 ft., and the ceiling outlets are 
located approximately 12 ft. apart. The watts per square foot 
for the main floor bays are slightly over 2 and the approximate 
mean horizontal foot-candles on a plane 33 in. from the floor with 
all lamps lighted, as shown by a test made upon a certain section 
of the main floor, were 9.3. The usual practice is to use only 
about one-half of the total lamps on this floor at any one time, 
and under these conditions the approximate mean foot-candles, 
for the section tested, were 5.5. Even with only one-half of the 
installation in use, the average illumination on the main floor of 
this department store is probably at least twice the average for 
stores of this type. In spite of this 100 per cent, increase in the 
quantity of illumination, the watts per square foot, on the basis 
of one-half of the lights being used, are no greater than for the 
ordinary arc lamp installation. The authors have data showing 
the watts of connected lighting installation per square foot of 
gross floor area — which includes walls, partitions, etc., but 
excludes any exterior or interior courts — for a number of large 
department stores. The figures range from a trifle over 1.4 
watts per square foot, in the case of a store where tungsten and 
tantalum lamps comprise a little over 15 per cent, of the total 
connected lighting installation, to a little less than .6 watt per 
square foot for a store in which tungsten and tantalum lamps 



80 



ENGINEERING FOR CENTRAL STATIONS 



form nearly 90 per cent, of the total connected lighting installa- 
tion. The values falling between these limits, however, show a 
considerable amount of variation from a strict relation between 
this wattage percentage and the number of watts per square 
foot of gross floor area. 

When it comes to the question of hours use per year of the 
total connected lighting installation, department stores — at least 
those in New York City that are supplied with central station 
service — show a remarkable degree of uniformity. In Fig. 15, 
the number of kilowatt hours consumed per year for lighting has 









































3 750,000 
3 










































































.ing Consumpl 
>watt Hours 

§ § 


















I 






J 


V 






























































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3^300,000 




















































Kilowatt Hours 1 Connected . 
-Consul per Lotion l*™ U ™\ , 
Year for Lighting | ^ Kilowatts ) (Approximately) 


» 150,000 




































1 




































1 















100 200 300 400 

Connected Lighting Installation in Kilowatts 

Fig. 15. — Showing the relation between the connected lighting installa- 
tion of a department store and the K. W. hours consumed per year for 
lighting. 

been plotted against the total connected lighting installation for 
four large department stores, in which it has been possible to 
separate the kilowatt hours used for lighting from those used for 
the operation of motors and for other purposes. It will be noted 
how close these four cases fall to a mean line, which gives a 
constant the value of which is 1867. In other words, the kilo- 
watt hours consumed per year for lighting in these four stores are 
approximately equal to the total connected lighting installation 
in kilowatts multiplied by 1867 hours. 

The monthly variations in the lighting requirements of a 
typical large department store are shown by the heavy full-line 
curve in Fig. 16. The lighting consumption during the month 
of December is always relatively high in department stores, as 
a result of such stores usually being open evenings for a week or 
more preceding Christmas, and also on account of the additional 



ELECTRICITY IN DEPARTMENT STORES 



81 



decorative lighting usually employed at this time. For this 
particular store, the December lighting consumption is approxi- 
mately 14 per cent, of the total yearly lighting consumption — 
which is perhaps slightly above the average for stores of this 
character. 

The subject of elevators, in its relation to the modern depart- 
ment . store, will next be considered. Until comparatively 
recently the hydraulic type of elevator was looked upon by the 



90.000 



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Jan. Feb. M; 



Apr. May June July Aug. Sept. Oct. ISJov. Dec. 



Fig. 16. — Showing the monthly variations in the lighting and power 
requirements of a large department store. 



majority of engineers as preferable to the electric type of elevator 
for department store service, and this fact is largely responsible 
for the prevalence of the former type of elevator in department 
stores at the present time. However, as a result of the improve- 
ments that have been made in the electric type of elevator during 
the past few years, there has been a decided change of opinion 
as to the comparative merits of these two types of elevators, and 
the electric type has now little to fear in this class of service 
from its once formidable hydraulic competitor. 

The accompanying table gives the results of a series of observa- 
tions made in connection with a study of the operation of the 
elevators in a number of large department stores. These observa- 
tions were made during what were considered to be periods of 
normal operation, and the figures given may therefore be taken 



82 



ENGINEERING FOR CENTRAL STATIONS 



Approxi- 
mate 
square feet 
of floor 
area per 
elevator 


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floors served 

by passenger 

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number of 

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running speed 

in feet per 

minute 

excluding 

stops 


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Running time 

as per cent, of 

total round 

trip time 


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seconds for 

complete 
round trip 


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Average 

number of 

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round trip 

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ELECTRICITY IN DEPARTMENT STORES 83 

as representing the average conditions of operation throughout 
the year. The number of elevators as given includes only those 
used by the public, and the total floor area as given is likewise 
confined to that portion to which the public has access. It will 
be observed that the percentage relation which the time spent 
in running bears to the total round trip time is a fairly constant 
quantity, the average value being 35 per cent. It will also be 
noticed that the running speeds of the elevators show a reason- 
ably close approach to an average speed of 200 ft. per minute. 
With these average values as a basis and with an estimated daily 
operating period of 10 hours, it would appear that the average 
distance travelled per day by a department store elevator is 
approximately 8 miles, a figure which the authors have sub- 
stantiated by actual mileage tests. 

A glance at this table will show that the traffic conditions in 
department store service are extremely severe — a stop being 
made at approximately every floor. As the amount of electrical 
energy consumed per car mile by the electric elevator depends 
very largely upon the number of starts and stops that are made, 
the kilowatt hours per car mile of travel are usually two or three 
times as great in the case of the department store elevator as 
they are for the same type of elevator in office building service, 
where the stops per car mile are ordinarily very much fewer in 
number. 

The dotted curve in Fig. 16 shows the amount of electrical 
energy consumed during each month of a recent year by eleven 
electric passenger elevators of the department store whose 
monthly lighting consumptions are shown by the heavy full-line 
curve. The light full-line curve shows the total power con- 
sumption by month, the difference between this curve and the 
curve shown by the broken lines representing the electrical 
energy used for operating four freight elevators and a number 
of miscellaneous motors, the latter aggregating a little over 100 
H. P. In this particular store the exhauster of the pneumatic 
tube system is normally operated by means of a steam engine, 
but a motor-driven exhauster is provided as a reserve unit. It 
will be observed that there is comparatively little variation 
throughout the year in the kilowatt hours consumed per month 
by this group of passenger elevators. The consumption of 
electrical energy per elevator per year for this group is about 
14,000 kilowatt hours. A test made upon these elevators during 



84 ENGINEERING FOR CENTRAL STATIONS 

July of the past year, showed the total travel for the month to be 
1764 miles. The average number of miles traveled per business 
day during this period by each of eight of these elevators — the 
combined mileage of which was 95 per cent, of the total — was 
7.6, while the average kilowatt hours per car mile were 6.7. 

Mechanical ventilation must be provided for the basement 
and sub-basement spaces of a department store if the floors 
below ground are to be devoted to sales purposes or if they 
are to be occupied by any considerable number of the store's 
employees. In some department stores the ground floor space 
is ventilated by mechanical means, but, as a general rule, the 
entire space above ground, with the exception of the toilets, etc., 
is ventilated by means of the windows, with the assistance, in 
some instances, of one or more ventilating ducts extending to 
the roof and having openings at each floor. 

Steam-driven ventilating fans are occasionally employed in 
stores of this character, but the motor-driven ventilating fan is 
the one most commonly found in this class of service. The 
yearly consumption of electrical energy by the motor-driven 
ventilating fans in a department store is necessarily high per 
connected motor horse-power, inasmuch as such fans are in 
operation during some 10 or 12 hours of each business day. 
During the winter season, the air supplied by these ventilating 
fans is, of course, tempered by first passing it through steam 
heated coils. Fans are either provided with a capacity sufficient 
to effect a definite number of air changes per hour in those por- 
tions of a department store that require mechanical ventilation 
— say, a complete change every 10 or 12 minutes — or else the 
capacity is based upon the number of persons that it is estimated 
will occupy the space requiring ventilation — a common allowance 
being some 30 cu. ft. of air per minute per person. 

In Fig. 17, the total yearly consumptions in kilowatt hours 
are plotted against the total gross volumes, above and below 
ground, of 16 department stores, some of which are located in 
New York City, some in Chicago and the remainder in Boston. 
A wide variation in the consumption of electrical energy is seen 
to exist when the several stores a e thus compared upon a 
volumetric basis. This is by no means surprising when it is 
considered that some of these stores have hydraulic elevators, 
while others have electric elevators; that some have arc and 
carbon lamp installations, while others have lighting installations 



ELECTRICITY IN DEPARTMENT STORES 



85 



consisting almost entirely of tungsten lamps — the watts per 
square foot of gross floor area actually ran ing for this group of 
stores from a little under .6 to something over 2.5 — and when 
it is further considered that some of these stores have a certain 
amount of steam-driven apparatus, while others use the electric 
drive throughout. This chart shows the futility of attempting 
to estimate the consumption of electrical energy in a given 
department store by comparing its cubical contents with those of 
another store of which the electrical consumption is known, 
unless careful attention is given to the many factors that tend 
to affect such a comparison. There is one point in connection 



M 

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B' 








































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5 10 15 

Gross Volume above and below Ground in Millions of Cubic Ft. 

Fig. 17. — Showing the relation between the gross volume and the K. W. 
hours consumed per year for a number of large department stores. 

with Fig. 17 to which the authors would direct particular atten- 
tion. The department store designated as "A" upon the chart 
has a complete electrical installation, which includes elevators 
and a large number of motors used for various purposes, and 
secures its supply of electrical energy from a central station. 
The store designated as "B" has a hydraulic elevator equipment 
and has its own private electrical generating plant. Although 
this store has a smaller gross volume than that of store "A," it 
will be observed that the annual consumption in kilowatt hours 
is over 50 per cent, greater than the consumption in store "A." 
The consumptions in these two stores tend to substantiate what 
the advocates of central station service claim; namely, that 
where a private generating plant is installed there is little or no 



86 



ENGINEERING FOR CENTRAL STATIONS 



incentive to the economical use of electrical energy, as a result of 
which a reasonably low unit cost of generation may actually 
mean a high total cost of providing the amount of electrical 
energy actually required. 

Fig. 18 shows three 24-hour load curves of a large department 
store. The full line curve represents the load throughout the 
24 hours of the day of maximum load, which occurred during the 

1400 



1200 



1000 



& 800 



13 60° 



400 



200 





























r\ 


































r 1 


\ 


Day of Maximum 
yLoad-Dec. 20th 


























1 
































/ 






























r 


Rainy Day 
in October 




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12 



12 



A.M. P.M. 

Fig. 18. — Showing typical daily load curves of a large department store. 



week prior to Christmas when this store was decorated profusely 
with incandescent lamps for the holiday season. The maximum 
load was reached at approximately 6 o'clock, which is about 
1 hour later than the maximum load on the generating plant of 
the central station supplying this department store. The other 
two load curves represent, respectively, a rainy day in October 
and a clear day in May. 

The yearly load factor of a department store, based upon the 
maximum load throughout the year and upon a year of 8760 
hours, is apparently about 30 per cent, when the electric type of 
elevator is used, and in the neighborhood of 23 per cent, when the 
elevator equipment is of the hydraulic type. These figures are 
for department stores supplied by central station service, and are, 



ELECTRICITY IN DEPARTMENT STORES 87 

of course, subject to a considerable amount of variation. Where 
a private generating plant is in use, the yearly load factor will be 
higher, as a result of the greater consumption due to the more 
wasteful use of electrical energy. The authors have in mind one 
department store, which has electric elevators and which operates 
its own generating plant, where the yearly load factor is 40 per 
cent. 

In addition to the strong argument in favor of a department 
store securing its supply of electrical energy from the central 
station on the ground of reliability of service, as mentioned 
earlier in this chapter, a private electrical generating plant is 
generally at a relative disadvantage in this type of building due 
to the fact that the amount of exhaust steam that can be utilized 
for heating the building is small compared with the total amount 
available from the generation of the very considerable amount of 
electrical energy that is usually required. In other words, the 
question of exhaust steam heating carries much less weight in a 
building of this character than it does in the average office 
building, where the amount of exhaust steam available from the 
electrical generating plant approaches more closely to the heating 
requirements of the building. 



CHAPTER IX 
THE PASSENGER ELEVATOR IN OFFICE BUILDING SERVICE 

The important rdle which the passenger elevator plays in our 
modern industrial life is probably realized by but comparatively 
few of the millions who daily depend upon this medium of 
vertical transportation. It is hardly necessary to call attention 
to the fact that the modern elevator has made possible the modern 
"sky-scraper/' which, in turn, has brought about, for better or 
for worse, that degree of industrial concentration which has been 
reached in some of our largest cities, with all the attendant 
difficulties as regards street congestion and over-taxed transporta- 
tion facilities. While it serves no useful purpose to speculate 
upon conditions as they might have been had the development of 
any particular piece of apparatus failed to occur, it is very evident 
that our large cities would have been far different from what 
they are to-day had not the elevator made its appearance when 
it did and undergone the development that it has. 

The figures which follow will convey some idea of the size of 
building that the modern elevator has made it commercially 
possible to erect, and they will also show how large the requisite 
number of elevators becomes in buildings of colossal size and 
tremendous height. The four largest office building structures 
in New York City will comprise, when the two last named are 
completed, the Hudson Terminal Buildings, the Whitehall 
Buildings, the Municipal Building and the Woolworth Building. 
The first two have gross volumes of 15 million and 11 million cu.ft., 
are 21 and 31 stories high and have 39 and 30 elevators 
respectively. The Municipal Building is to be 40 stories high, 
is to contain something over 18 million cu. ft. and is to have a 
total of 33 elevators, while the Woolworth Building is to have a 
total of 55 stories above ground, is to contain some 13 million 
cu. ft. and is to have a total of 34 elevators. The elevators in all 
of these four buildings either are or will be of the electric traction 
type. To give some idea of the immensity of the transportation 
requirements in a building of the size and character of those cited, 
it will be pointed out that some 40,000 persons are said to be 
carried per day by the 39 elevators in the Hudson Terminal 

88 



ELEVATORS IN OFFICE BUILDINGS 89 

Buildings. The combined daily travel of all the elevators in the 
four buildings mentioned will, undoubtedly, be at least 3500 miles 
— a distance substantially equal to that which separates New 
York and London. 

The development of the elevator from its inception to the 
present time affords a subject of considerable interest, but it 
will be treated herein only to such an extent as will serve to show 
the sequence in which the several types of elevators come into 
use, and to bring out the characteristic features of those types 
which have survived. 

The first type of passenger elevator to be used in this country 
was operated by means of steam. This was a half century or 
more ago, when buildings were only some three or four stories in 
height. The operation of this type of elevator was too slow to 
be of much service, and it was not until the advent of the hy- 
draulic elevator that the height of buildings underwent any 
material increase. One of the first forms of hydraulic elevator 
was known as the " water-balance" type, and it was installed in 
a number of buildings in different parts of the country. In this 
type the car was suspended by cables which passed over sheaves 
at the top of the elevator shaft and were fastened to an iron 
bucket which weighed less than the car and which was free to 
move in a vertical iron pipe. By means of a hand cable which 
passed through the car and which connected with valves, the 
operator could admit water to or discharge it from the bucket, 
and in this way could cause the car to ascend or descend. Brakes, 
acting upon the guide strips, were provided for controlling the 
speed of the car, but no automatic devices were employed. 
While this type of elevator was capable of high speed, it 
proved decidedly dangerous in operation and its use was soon 
discontinued. 

In 1878 the vertical-cylinder type of hydraulic elevator was 
first installed in New York City, and although this type has since 
been considerably improved in detail, it is substantially the same 
in principle as when first introduced, and it represents to-day the 
most common type of hydraulic elevator. In its present-day 
form, this type of elevator comprises a vertical cylinder located 
along one side of the elevator shaft and usually limited in height 
to approximately 30 ft. This vertical cylinder contains a piston 
which is connected by rods to a traveling frame in which sheaves 
are mounted. Fixed sheaves are located at a sufficient height 



90 ENGINEERING FOR CENTRAL STATIONS 

above the traveling sheaves to accommodate the piston stroke, 
and the cables which are attached to the car first pass over 
sheaves at the top of the elevator shaft, then down around the 
traveling sheaves, then up and around the fixed sheaves, down 
again to the traveling sheaves and then up to the fixed sheaves 
where their ends are anchored. By thus passing the cables back 
and forth between the traveling and fixed sheaves, a tackle is 
formed which multiplies the stroke of the piston by an amount 
equal to twice the number of traveling sheaves. This is known 
as the "gear," and it represents the ratio of car travel to piston 
travel. By means of this "gear" this type of elevator has been 
employed for a rise of over 300 ft. This type of machine has 
been installed to operate with water pressures ranging from less 
than 100 lb. to 750 lb. or more per square inch. The high-pres- 
sure installations usually show a somewhat higher economy as a 
result of a reduction in the hydraulic losses. Two-pressure 
systems — a high water pressure for heavy loads and a low 
water pressure for light loads — have been installed in a few 
instances in order to obtain an increase in efficiency as a result of 
more closely adapting the work of the elevator to the load that is 
being carried, but the added complication of this arrangement 
has resulted in a very limited application. 

The horizontal cylinder elevator is quite similar in principle to 
the vertical type just described, but it has not been used to any- 
where near such an extent as the latter. It is found in two forms 
known as the "pushing" and the "pulling" types, the latter 
being essentially the same as a vertical type machine laid on its 
side. In order to save space the "gear" of these machines is 
usually considerably higher than that common in vertical type 
machines. In the vertical-cylinder type of elevator the weight of 
the car and live load is partially balanced by the weight of the 
piston and traveling sheaves, to which is added a certain amount 
of counter-weight, leaving the amount of unbalance sufficient to 
cause the car to descend at a proper rate of speed when it con- 
tains the operator alone, and to come to a stop when ascending 
with a light load within the proper distance. In the horizontal- 
cylinder type no assistance is obtained from the weight of the 
piston and traveling sheaves so far as balancing the weight of the 
car and its load is concerned. It is therefore necessary to provide, 
with this type of elevator, an independent counter-balance 
attached to the car by means of separate cables. 



ELEVATORS IN OFFICE BUILDINGS 91 

The electric elevator first appeared upon the scene in the year 
1887, when a direct-connected machine, designed by Mr. William 
Baxter, Jr., was installed in a building in Baltimore. This 
elevator was of the worm-gear drum type, with a constant cur- 
rent, series-wound type of motor, operated from a Brush arc 
light circuit. It does not appear that this particular type of 
electric elevator was tried elsewhere than in the installation 
referred to. Two years later, two electric elevators of the drum 
type, operated by compound motors with fixed shunt fields, 
were installed in a building on Fifth Avenue, New York City. 
These elevators were designed by Mr. N. P. Otis, while the elec- 
tric features were the design of Mr. Rudolph Eickemeyer. This 
type of machine proved successful and other installations followed 
rapidly. From this time until the year 1894, when the screw- 
type electric elevator, with pilot motor control, was brought out 
by Mr. Frank J. Sprague and Mr. C. F. Pratt, all electric elevators 
continued to be of the drum type. While this screw-type 
machine was popular for a time, and while it was installed in a 
number of prominent buildings, it proved more costly to main- 
tain and it required a higher consumption of electrical energy 
than the drum type machine. Although the manufacture of 
these machines has long since been discontinued, quite a number 
of them are to be found in operation in New York City to-day. 
The first drum type elevators were one-speed machines. Efforts 
to obtain variable speed resulted in the development of the Ward- 
Leonard system, which has been used quite extensively, although 
it involves a considerable amount of complication. This system 
of control requires a separate generator for supplying current to 
each motor armature, the shunt fields of both the generator and 
motor being supplied with energy from a separate source. By 
varying the shunt field of the generator, the current supplied to 
the armature of the motor can be very effectively controlled, 
without incurring the heavy rheostatic losses which result from 
direct armature control. In 1897 the magnet system of control 
was developed, the action of which depends upon the counter 
electro-motive-force developed by the motor as its speed increases, 
the resistance in series with the armature, and finally that in 
series with the field, being gradually cut out by means of a series 
of magnets. 

By the late nineties we therefore see that the electric elevator, 
as represented by the drum-type machine, was in a position to 



92 ENGINEERING FOR CENTRAL STATIONS 

effectively compete with the hydraulic elevator of the vertical 
and horizontal-cylinder types, except in the case of very high 
buildings. For very high rises, the Sprague screw type was 
available, and this type of elevator was installed in several of 
the highest buildings erected at this period, among which may 
be mentioned the 32-story Park Row Building, New York City, 
in which the 10 passenger elevators, with a rise of 2.6 stories, are 
of the Sprague vertical screw type. 

The reason why the drum type of elevator is unsuitable for 
buildings of great height is because of the excessive size of the 
drum required under these conditions. The four cables which 
wind upon the drum — two of which lead to the car and two to 
the counter-weight — require about 3 in. of drum width for each 
revolution of the drum. As a drum 3 ft. in diameter has a 
circumference of about 10 ft., a 20-story building would require 
about 25 revolutions of a drum of this diameter, and therefore 
a drum of over 6 ft. in length would be required. With the car 
at the top or bottom of the shaft, the cables would be at alternate 
ends of the drum and hence some 3 ft. off from a vertical line 
drawn through the center of the drum and the overhead sheaves. 

Several different types of electric elevators soon appeared, all 
designed with the idea of eliminating the drum winding and thus 
removing the limitation upon the height of travel which the 
drum winding imposed. Before following the development of 
the electric elevator further, however, we will turn for a moment 
to a type of hydraulic elevator which became available for high 
rise work at this juncture and before a satisfactory form of 
non-drum type elevator was developed. 

It was about 1899 that the plunger type of hydraulic elevator 
became prominent in connection with high-rise work. This type 
of elevator was by no means new at that time, as it had been 
used extensively in Europe for some time for buildings of moder- 
ate height, and also to some extent in this country, particularly 
for the handling of freight. The use of this type of elevator for 
passenger service in very high buildings was made possible at 
this time as a result of the adoption of improved methods of 
accurately drilling the deep holes required, thereby reducing to 
some extent the cost of installation; also by the use of a hollow 
plunger and heavy ropes connecting the car and counter-weight, 
so that as the car ascends, the weight of these ropes, being 
transferred to the side of the counter-weight, overcomes the 



ELEVATORS IN OFFICE BUILDINGS 93 

variation in water pressure which results from the plunger dis- 
placement and which is very considerable in the case of high 
rises. For several years this type of elevator enjoyed a con- 
siderable degree of popularity, and it was installed in a number 
of high office buildings in New York City and elsewhere. It was 
also installed in a number of prominent hotels, department stores, 
etc., and for use in buildings of this character it has a large 
number of advocates at the present time. For high-rise office 
building work, where high elevator speeds are involved, the 
plunger type of elevator has now been practically superseded, 
so far as new installations are concerned, by an electric form of 
elevator known as the 1:1 traction type. The chief advantage 
claimed for the plunger type of elevator is that of safety in 
operation. Where heavy loads are handled at low speeds this 
claim is probably justified, but for high-rise work at high speeds 
the safety of this type of elevator is not enough greater than that 
of other types, when the latter are properly installed, to justify 
the increased feeling of security that is frequently engendered in 
the lay mind as a result of the car being supported from beneath 
instead of being suspended from overhead. The plunger 
elevator, in common w T ith all elevators of the hydraulic type, 
depends upon gravity to effect retardation on the up-trip and to 
cause the car to descend. This means that the car must be 
sufficiently under counter-weighted to effect a stop when ascend- 
ing with a light load within a reasonable distance, and to cause 
the car to descend, under the same conditions, at a proper rate 
of speed. As the operating speeds become greater, the difficulty 
of effecting proper retardation by means of gravity is enormously 
increased, and in the case of the plunger type of elevator the 
weight of the moving parts becomes so great in a high-rise installa- 
tion as to make it difficult or impossible to make landings with 
precision when running at a high rate of speed. This difficulty 
materially decreases, therefore, the average service speed attain- 
able with this type of machine. 

The 1:1 traction type of elevator, to which reference has 
already been made, was developed some 7 or 8 years ago, and 
this type of elevator now promises to become the standard for 
high-rise, high-speed work. The operating mechanism of this 
elevator is extremely simple, consisting of a slow-speed motor 
direct-connected to a grooved wheel. Vertically above or below 
this wheel, according to whether the motor is located at the 



94 ENGINEERING FOR CENTRAL STATIONS 

bottom or top of the shaft, is placed an idler, and the ropes con- 
necting the car and the counter- weight pass over this grooved 
wheel, then around the idler and then back over the grooved 
wheel. The weight of the car and the counter-balance produce 
sufficient adhesion between the ropes and grooved wheel to 
cause the former to move with the latter at its circumferential 
speed. This type of elevator possesses a number or advantages 
over the drum-type machine. As compared with the latter, it 
has the advantage that the ropes are always in a vertical position, 
and that there is no danger from overrunning at the top or 
bottom of the shaft; for if the motor should continue to revolve 
after the car has reached the end of the up-t ravel, the counter- 
weights would have reached the lowest point of their travel and 
the ropes would therefore slacken and permit the motor to revolve 
without causing any further movement of the car. At the end 
of the down trip the same conditions would result from the car 
reaching the lower end of its travel, whereupon the ropes, being 
relieved of the weight of the car, would slacken and the motor 
could still continue to revolve without producing any harmful 
results. The 1:1 traction elevator requires a motor of very 
slow speed — about 60 r. p. m. as a rule — and in order to over- 
come this feature the worm-gear traction machine has been 
developed, which permits of the use of a motor of standard speed, 
thereby resulting in a somewhat higher motor efficiency and a 
lower motor cost. In principle this machine is similar to the 
1:1 traction, the only difference being that worm-gearing is 
interposed between the motor shaft and the shaft carrying the 
grooved wheel over which the cables pass. 

In what has preceded, an attempt has been made to cover, 
somewhat briefly, the development of the elevator from the time 
of its first appearance up to the present time. The discussion 
has been confined to those types of elevators that have proven 
successful in operation; and no attention has been paid to certain 
other types that have been tried, but, for one reason or another, 
have not proven altogether satisfactory. As the matter stands 
to-day, the electric type of elevator possesses several advantages 
over the hydraulic type of elevator: first, because it is cheaper 
to install, and, second, because it is cheaper to operate, provided 
electrical energy is obtainable at a reasonably low cost. So far 
as the question of safety is concerned, there is probably little to 
choose between the electric and the hydraulic types to-day, if 



ELEVATORS IN OFFICE BUILDINGS 95 

both are properly installed and carefully maintained, and if the 
traction instead of the drum-type of electric elevator is selected 
for comparison in cases where the speed and rise are high. 

As previously mentioned, the hydraulic elevator must always 
be considerably under counter-weighted in order that gravity 
may stop the car when ascending without load when the power is 
shut off, and in order that it may cause the car to descend at 
proper speed when lightly loaded. This usually means that the 
weight of the counter-balance can only be about two-thirds of 
the weight of the car. In the case of the electric elevator, how- 
ever, power is used for both raising and lowering the car, and the 
counter-balance may be designed not only to balance the weight 
of the car itself, but also the average live-load carried. As a 
result of this, the amount of power required for a given weight of 
car and live-load is very much less in the case of the electric than 
in the case of the hydraulic elevator. 

The drum type of electric elevator is provided with two, and 
frequently with three, different forms of counter- weight; while 
other types of elevators are provided with one and sometimes 
with two forms. One counter-weight of the drum-type machine 
usually balances approximately two-thirds the weight of the 
empty car, the cables connecting the car and the counter-weight 
passing over one of two over-head sheaves. This arrangement 
tends to keep these cables in tension, and it thereby reduces the 
tendency of the car to bounce, when the rotation of the drum is 
stopped. The second counter-weight balances the remainder of 
the car's weight and usually the estimated average live load, 
which is generally taken at from 20 to 40 per cent, of the maxi- 
mum carrying capacity of the car. Occasionally the live-load 
counter-weight is increased to 50 per cent, of the maximum load 
that the car can carry, in order to keep the starting current at 
a minimum. This is sometimes necessary when the current is 
to be obtained from an isolated plant which is also to supply 
current for lighting from the same generator or generators. The 
third form of counter-weight referred to in connection with the 
drum-type machine, and the second in connection with other 
types of elevators, is a varying counter-weight, usually in the 
form of a chain composed of heavy links. The purpose of this 
counter-weight is to balance the varying weight of the cables on 
the two sides of the overhead sheaves. One end of the chain is 
fastened to the bottom of the car. while the other end is made 



96 



ENGINEERING FOR CENTRAL STATIONS 



fast to the bottom of the regular counter-weight. As the car 
ascends, more and more of the weight of the chain is transferred 
from the counter-weight to the car, and as the car descends the 
reverse occurs. By this means it is possible to counteract any 
variation in the power requirements due to the weight of the 
cables being transferred from one side to the other of the overhead 
sheaves. It is quite usual to make the weight of the chain 
somewhat greater than the weight of the cables, for the reason 
that the car is usually most heavily loaded when at the bottom 
of the shaft, the live load decreasing as the car ascends 











^ 


























377 








5 


































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per 


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1500 



300 



1200 900 600 

Weight of Live Load in Lbs. 

Fig. 19. — Showing how the consumption of electrical energy per car 
mile is affected by the number of stops made per mile and by the amount 
of unbalanced live load that is being carried. 

The use of the term "kilowatt hours per car mile," as a meas- 
ure of electric elevator performance, was apparently introduced 
into elevator parlance by Mr. Frank J. Sprague, who, prior to his 
entrance into the elevator field, was actively identified with the 
development of the electric railway. As a unit for comparing 
the operating efficiency of electric elevators under different serv- 
ice conditions, it leaves much to be desired. The kilowatt 
hours per car mile are dependent upon a number of variables; 
for instance, they depend upon the speed and load conditions, 
upon the number of stops and starts per mile, upon the amount 
of unbalanced load that is being carried, and upon several other 
factors of somewhat less importance. 



ELEVATORS IN OFFICE BUILDINGS 



97 



Fig. 19 shows the variation in kilowatt hours per car mile in 
the case of a direct current drum-type elevator carrying dif- 
ferent amounts of live load and making different numbers of 
stops per car mile. The elevator in question is one of seven 
which serve an office building which has a total of 15 stories above 
the ground floor. The amount of live-load counter-balance is 
approximately 750 lb., and tests, with four different numbers 
of stops per round trip, w T ere made with live loads of 150, 600, 
925, 1350 and 1580 lb. The kilowatt hours per car mile for each 
test were obtained by means of a graphic ammeter, supple- 
mented by a volt-meter. While the figures given may be subject 



o 

— _ ^ 

4 o 

^_o 

o 
3 o 

Q !! 

o 

2 ' : I I 

Q 

O 



75 100 125 

Rating. of Motor in Amperes at 220 Volts 



150 



Fig. 20. — Showing the relation between the K. W. hours per car mile and 
the rating of the elevator motor in amperes. 



to some slight error of observation or calculation, they are suffi- 
ciently accurate to show the effect produced upon the kilowatt 
hours per car mile by the number of stops and starts and by the 
amount of unbalanced live load that is being carried. The 
effect of the former is very marked, and it explains why the con- 
sumption of electrical energy per car mile is usually so much 
higher in the case of a department store or similar building, where 
the elevators stop at practically every floor, than in the case of 
an office building where the stops usually average three or more 
floors apart. 

Fig. 20 shows the actual average kilowatt hours per car mile in 
13 office buildings where direct-current drum-type machines are 



98 ENGINEERING FOR CENTRAL STATIONS 

in use. These consumption figures were obtained from tests 
covering two or more weeks, and the values as given cover normal 
business day operation only, Sundays and holidays being ex- 
cluded. This was done in order to eliminate any uncertainty re- 
sulting from an increased consumption per car mile due to the 
motor fields being energized during periods of almost complete 
idleness. It will be observed that the kilowatt hours per car mile 
increase with considerable uniformity as the rating of the motor 
, increases. This is, perhaps, to be expected in the case of buildings 
of similar type and in which the conditions of operation are 
substantially the same, provided the motor ratings are properly 
adapted to the different speed and load requirements of the 
several buildings. 

The accompanying table, Insert 2, contains data upon the ele- 
vator equipments of 25 office buildings, all but a few of which are 
located in New York City. It will be seen from this table that the 
square feet of floor area served per elevator and per square foot 
of total car area vary considerably in different buildings, even 
where the number of floors served is substantially the same. 
Where there are express as well as local elevators, the square feet 
of floor area served per elevator and per square foot of car area 
are not given for the reason that it would be difficult to properly 
express these relations. It will be observed that the average 
round trip running time in minutes of the elevators in these 
buildings, including all stops, shows a considerable degree of 
uniformity. 

Fig. 21 shows the average number of miles traveled per busi- 
ness day by the elevators in some 20 office buildings. The 
diagonal lines represent different round trip times, based upon a 
mean distance of 12 ft. between floors and upon an operating day 
of 10 hours, which is the usual number of hours per day during 
which elevators are operated in office buildings. In the buildings 
of 10 stories and under, the average round trip time, including 
all stops, is about 13/4 minutes. As the number of stories 
become greater, the round trip time falls off to a slight extent, 
and the average speed, including stops, is seen to remain fairly 
constant. For buildings ranging from 15 to 19 stories the average 
round trip time is seen to be around 2 1/4 minutes, but the 
average speed increases from about 150 to something over 200 ft. 
per minute. This increase in the average speed is due to the 
use of higher speed machines in the higher buildings and to a 



















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OFFICE BUILDING ELEVATOR DATA 




























































































































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ELEVATORS IN OFFICE BUILDINGS 



99 



reduction in the number of stops per car mile as the number of 
floors served by the elevator increases. 

The upper floors of our high office buildings offer superior 
advantages in the way of light and air over the floors located 
near the street level, but unless he time occupied in reaching 
these floors is reduced to approximately that required in reaching 
the lower floors, the former are placed at a disadvantage from a 
rental standpoint. It is for this eason that higher speed ele- 



24 



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12 14 16 

Number of Stories above Ground Floor 



20 



Fig. 21. — Showing round trip time and average speed of local elevators in 
office building service. 



vators become necessary as the heights of buildings increase, and 
express service usually becomes necessary for the upper floors of 
buildnigs exceeding some 15 or 16 stories in height. In one par- 
ticular office building in New York City, local elevator service is 
employed for a rise of 26 stories, with the result that the average 
round trip time is prolonged to nearly four minutes, which can 
hardly be viewed as satisfactory service so far as the upper floors 
of this building are concerned. The tra tion type elevator, with 
its rapid acceleration and with its ability to carry loads at close 
to rated speed, is particularly suited for the high speed work now 
required to maintain a satisfactory round trip time in buildings 
of extreme height. The ascending speed of the hydraulic 
elevator, on the other hand, falls off rapidly as the live load is 



100 ENGINEERING FOR CENTRAL STATIONS 

increased. Under the service demands that usually occur in 
office buildings in the early morning, as a result of nearly all of 
the occupants of the building arriving and demanding trans- 
portation to their offices within a comparatively short period of 
time, the hydraulic elevator, ascending heavily loaded and 
descending practically without load, is at a decided disadvantage 
as compared with an elevator of the electric type and the round 
trip time of the former becomes unavoidably extended at such a 
time. If the elevator requirements of a building are based upon 
furnishing transportation for all of the building occupants within 
a certain specified time of arrival, say, within a period of 20 
minutes or 1/2 hour, more elevator capacity will be required 
with the hydraulic type of elevator than with an elevator of the 
electric type, where both types are designed for the same average 
speed under normal traffic condlt ons. 

Fig. 22 shows a chart by means of which the number of square 
feet of car area may be obtained when the total square feet of 
rentable office area are known, for any assumed period within 
whi h all of the occupants of the building must be transported 
in one directi n. This chart is based upon an allowance of 2.25 
sq. ft. of car area per occupant, not including the car operator, 
which closely represents the maximum carrying capacity of an 
< levator car without excessive crowding. One hundred square 
feet of occupied floor area has been allowed per person, which is 
an average figure for New York City office buildings, but this 
chart may be used for any other assumed density of occupancy. 
In order to show the application of this chart, a proposed building 
will be worked out in detail. 

Suppose we have a proposed office building which is to have 
a total occupied floor area of 80,000 sq. ft. and a total of 16 stories 
above the ground floor. Referring to Fig. 21, we can reasonably 
assume an average round trip time for a building of this number 
of stories of about 2 1/4 minutes, but during the early morning 
rush we will permit of a slight extension of the schedule and fix 
the maximum round trip time under these conditions at 2 1/2 
minutes. We will assume that the elevator capacity is to be 
sufficient to handle all of the building occupants one way within 
a period of 1/2 hour. If we now follow a perpendicular line 
through the point 2.5 on the scale of round trip time until it 
meets the curve marked "30 minutes," and from the point of 
intersection draw a horizontal line to the left until it meets a 



ELEVATORS IN OFFICE BUILDINGS 



101 



vertical line erected at 80,000 sq. ft. of occupied floor area, we 
locate a point practically midway between the diagonal lines 140 
and 160. This means that a total car area of 150 sq. ft. must be 



180.000 




Fig. 22. — Showing a chart for determining the number of elevators required 
to serve an office building of known occupied floor area. 

provided to meet the conditions that have been assumed. We 
follow a diagonal line drawn midway between the lines 140 and 
160 until it meets the corresponding curve line; then by following 
this curve both up and down we obtain various combinations of 



102 ENGINEERING FOR CENTRAL STATIONS 

car area and number of cars that will provide a total car area of 
the required amount, namely 150 sq. ft. By selecting the size 
of car which ^e desire — which is occasionally governed by the 
dimensions of the space that is available and, to some extent, by 
the number of stories served — we can determine at once the 
number of cars of the selected size that will be necessary. For 
our assumed case, if we select a car having 30 sq. ft. — a size that 
is quite common — we find that we will require five such cars; by 
selecting a car of 37 sq. ft., the number of cars required would be 
reduced to four, and by using a car of 25 sq. ft., the requisite 
number of cars would be increased to six. If we had a different 
density of occupancy, say 125 sq. ft. per person, it would only 
have been necessary to take a point 25 per cent, higher on the 
scale of occupied floor area per square foot of car area than that 
determined by the intersection of the horizontal line drawn from 
the 30 minute curve, and then draw our horizontal line to the 
left from this new point until it meets the vertical line drawn 
through the number of square feet of occupied floor area. By 
means of this chart the number and size of the elevators required 
for a given office building may be readily determined to meet any 
given operating requirements, and the elevator builder should 
then be required to guarantee the fulfillment of the round trip 
time as specified, under the conditions of maximum traffic that 
have been assumed. 



CHAPTER X 
OZONE : ITS PRODUCTION AND UTILIZATION 

The word " ozone" is derived from a Greek root, which 
corresponds in meaning to our English word "smell." The 
correctness of this derivation becomes apparent as soon as one 
smells ozone for the first time, for it possesses a decidedly char- 
acteristic odor, resembling somewhat, in high dilutions, that of 
chlorine, and, when in a more concentrated form, that of moist 
phosphorous. While the odor of this gas is not particularly 
pleasant, it is not, on the other hand, of a character that could 
ordinarily be termed obnoxious, unless, perhaps, when it is 
present in much greater quantity than is required for the puri- 
fication and disinfection of air. Moreover, as ozone cannot 
exist, except momentarily, in contact with organic matter, its 
presence in the air is only perceptible after the air has reached a 
sterile condition. Even if an excess of ozone is present, its odor 
is certainly far preferable to that fetid smell so noticeable when 
a considerable number of people are congregated in a poorly 
ventilated room, and which results from the presence of decaying 
organic matter in the air that has been expired. The odor of 
ozone is perceptible in extreme dilutions with air. It is stated 
that the ordinary person can detect the presence of this gas when 
it is mixed with air in the proportion of 1 to 10,000,000 parts by 
volume, which is equivalent to a concentration of .00001 of 1 
per cent. 

Ozone is a colorless gas with the chemical symbol 3 , the mole- 
cule possessing one more atom than the oxygen molecule, which 
is expressed by the symbol 2 . In the presence of oxidizable 
matter, such as organic substances, ozone is immediately decom- 
posed, the third atom combining with the oxidizable matter to 
form a more stable compound, while the two other atoms remain 
in combination to form the ordinary oxygen molecule. Ozone 
is, therefore, oxygen in a condition of great chemical instability, 
and as a result of this instability in the presence of oxidizable 
substances, we have in ozone the most active oxidizing agent 
known. 

103 



104 ENGINEERING FOR CENTRAL STATIONS 

The discovery of ozone is usually credited to the Dutch 
physicist Van Marum, who, about the year 1785, while studying 
the effects produced by electrical discharges upon various gases, 
noted that oxygen, when subjected to these discharges, gave off 
a decided odor. It was not until 1840, however, that oxygen in 
the peculiar form now known as ozone, was recognized as a 
distinct gas. In the year mentioned, or thereabouts, a German 
chemist by the name of Friedrich Schonbein, who was a professor 
at the University of Basle, in Switzerland, observed the peculiar 
chemical properties possessed by oxygen after having been 
subjected to electrical stress, and to this modified form of oxygen 
he gave the name " ozone." 

During the 50 years which followed, this gas continued to be 
of scientific interest only, and while its production on a small 
scale was readily effected by electrical or chemical means in the 
laboratory, it was not until the French chemist Berthelot took 
up the study of this gas in 1890, with the purpose of applying 
its then well-recognized properties to practical ends, that the 
development began which has given to ozone the commercial 
importance which it has now attained. 

There are a number of different methods, chemical and 
physical, that have been resorted to in the production of ozone, 
but only one of these methods is practicable so far as its pro- 
duction on a commercial scale is concerned. To cite a few of 
the different methods that have been employed, it may be men- 
tioned that ozone has been produced (1) by the electrolysis of 
certain liquids, such as water and sulphuric acid; (2) by the 
action of strong sulphuric acid upon permanganate of potash; 
(3) by the addition of fluorine to water; (4) by the oxidation of 
phosphorous by moist air; (5) by the oxidation of certain essen- 
tial oils, such as turpentine; (6) by subjecting air or oxygen to 
sudden and extreme changes in temperature, the air or oxygen 
being first led over an incandescent body and then suddenly 
cooled by means of liquid air; (7) by means of the radiations 
from radioactive salts; (8) by the action of ultra-violet rays upon 
air, these rays being produced by means of the mercury arc in a 
quartz tube; and (9) by subjecting air or oxygen to electric 
stress or discharge. 

Nature produces ozone in her own laboratory in immense 
quantities, although the amount actually present in any locality 
is extremely minute when compared with the volume of the air 



OZONE: ITS PRODUCTION AND UTILIZATION 105 

with which it is diluted. Ozone is usually present in greatest 
quantity in regions of thick forest growth, particularly in high 
altitudes, and near large bodies of water from which the amount 
of evaporation is considerable. Mountain air and that of the 
seashore as well are commonly believed to derive a considerable 
part of their health-giving properties from the presence of this gas 
in greater quantity than that usually obtaining in other regions. 
In cities and towns, on the other hand, oxidizable matter is 
always present in sufficient quanities to preclude the presence 
of ozone in the air. While various authorities have placed 
different estimates upon the quantity of ozone that is present 
in the air in different localities and under various conditions, it 
is improbable that the amount present in any locality ever ex- 
ceeds 1 part in 1,000,000 parts by volume of air. As previously 
noted, however, very much higher dilutions than this can readily 
be detected by the sense of smell. 

While the methods mentioned above, and possibly some others 
as well, have been employed in the production of ozone, the 
method last mentioned affords the only practical means of pro- 
ducing this gas in any considerable quantity at the present time, 
and this condition is the direct result of the developments in 
electrical apparatus which have occurred during the past 20 
years, and more particularly the development of those two pieces 
of apparatus known as the alternating current generator and the 
high-tension static transformer, which, in combination have 
made it commercially practicable to produce electrical energy in 
quantity and at high potential. While early experiments showed 
that small quantities of ozone could be produced by electric stress 
or discharge at low potential, it soon became apparent that pro- 
duction in quantity, with due regard for efficiency, required the 
employment of high potential. At first these high potentials 
were obtained by means of static electrical machines or induction 
coils operated by primary batteries, but the apparatus thus 
required was cumbersome and the cost of producing electrical 
energy by these means was too great to permit of its being 
applied to any commercial uses which required any considerable 
amount of electrical energy. The alternating current generator 
and the static transformer, however, solved the problem of sup- 
plying electrical energy in any amount at high potentials without 
the necessity of employing the bulky and expensive apparatus 
that had hitherto been required. 



106 ENGINEERING FOR CENTRAL STATIONS 

Before attempting to describe the characteristic features of 
several of the more important types of ozonizers that have been 
developed, it will, perhaps, be well to mention that, when air or 
oxygen, is subjected to electrical stress or discharge, there are 
certain surrounding conditions which affect materially the 
amount of ozone that will result from a given input of electrical 
energy. 

The temperature of the air, when subjected to electrical stress 
or discharge, has a very important bearing upon the amount of 
ozone that will be produced, due to the fact that the instability 
of ozone increases with the temperature. In order to keep the 
temperature o the air as low as possible while undergoing elec- 
trification, different methods have been resorted to, such as 
cooling the electrodes by means of water, the use of mechanical 
refrigeration, etc., to which further reference will be made in 
describing some of the types of ozonizers now in use. This 
temperature effect also explains the increase in efficiency which 
results from the use of electrical energy at high potential as com- 
pared with low potential, inasmuch as the heat produced by the 
discharge varies as the square of the current, while the current, 
for a given number of watts per unit of air ozonized, varies in- 
versely as the voltage. In order to obtain the high outputs and 
concentrations that are now required where ozone is used for 
industrial purposes, it becomes necessary, therefore, to use a 
high voltage in order that the amount of heat produced may be 
reduced to a minimum. While there are practical limits to the 
maximum voltage that may be used, 8000 to 10,000 volts are 
now considered about the minimum that can economically be 
employed when both a high yield and a high concentration are 
required. 

The presence of moisture in the air undergoing electrification 
tends to reduce materially the amount of ozone produced, and 
for this reason it frequently becomes necessary to dry the air 
before ozonizing it, except in the case of very low concentrations, 
such as obtain when the ozone is to be used simply for the 
purification of air. The method most commonly employed for 
removing an excess of moisture from the air consists of passing 
the air over lime or over some other moisture-absorbing substance, 
although in certain ozone plants of large output mechanical 
refrigeration has been resorted to to "freeze" the moisture out 
of the air. 



OZONE: ITS PRODUCTION AND UTILIZATION 107 

The production of ozone by means of an electric discharge is 
always accompanied by the formation of certain oxides of nitro- 
gen in greater or less amount. The formation of these oxides is 
highly undesirable, particularly when the ozone is to be used for 
the purification of air, and, for this reason, designers of ozonizing 
apparatus have given much attention to the problem of prevent- 
ing, as far as possible, the formation of these oxides. As a result 
of this, in well-designed ozonizers at the present time, the amount 
of nitrous oxides formed does not ordinarily exceed some 1 or 2 
per cent, of the amount of ozone produced and, when the yield 
and concentration are both low, may even be considerably less 
than this. On the other hand, in apparatus of poor design, the 
amount of these oxides may reach 5 or even 10 per cent, of the 
amount of ozone generated. 

As heat, sparks, dust and moisture are all favorable to the 
formation of these nitrous oxides, the importance of maintaining 
a low temperature is still further accentuated, and the necessity 
of preventing the formation of disruptive discharges or sparks, 
instead of the so-called cold or silent discharge, becomes readily 
apparent. As the presence of dust and dirt favors the formation 
of sparks, it is important that the entering air should be as free 
from dust as possible and that accumulations of dirt within the 
ozonizer should be prevented. 

The term "yield," as applied to the production of ozone, is 
used to signify the amount of ozone produced per unit input of 
electrical energy, and it is measured in grams (a gram being 
equivalent to .0022 of a pound) per K. W. hour. The term 
" concentration" is employed to express the quantity of ozone 
produced per unit quantity of air, and this is generally expressed 
in grams of ozone per cubic meter of air (a cubic meter being 
equivalent to 35.3 cu. ft.). Unfortunately, with our present 
types of ozonizers, a high concentration is obtainable only by 
sacrificing to a greater or less extent the amount of yield, and 
the efficiency of any given ozonizer will therefore decrease as 
the concentration of the ozone produced is increased. This, of 
course, is due to the heating effect of the discharge, to which 
reference has already been made. When an ozonizer is being 
operated so as to give a high concentration, the wattage of the 
electrical discharge per unit of air ozonized is necessarily high, 
which means either a reduced flow of air or an increase in the 
electrical discharge per unit of electrode surface, as compared 



108 ENGINEERING FOR CENTRAL STATIONS 

with the conditions obtaining when only a moderate amount of 
concentration is required. On the other hand, when the volume 
of the air which passes through an ozonizer is increased, the 
amount of ozone per unit volume of air becomes less, but as this 
larger quantity of air serves to maintain a lower temperature in 
the space through which the electrical discharge takes place, the 
amount of yield undergoes an increase. 

In order to give some idea of the rapid development which 
has taken place in the production of ozone by electrical means, 
it may be mentioned that the ozonizer employed by Berthelot 
in 1890 was capable of giving a yield of 1 grm. per K. W. hour 
and a concentration of .5 grm. per cubic meter of air; while by 
the year 1909, one commercial type of ozonizer was credited 
with a maximum yield of 100 grm. per K. W. hour and with a 



Ozone- 



1 



Fig. 23. — Berthelot ozonizer. 



maximum concentration, at lower yields, of 30 grm. per cubic 
meter of air. Since 1909, even higher yields have been reported, 
and it is claimed for one type of ozonizer that a yield of 250 grm. 
per K. W. hour has been obtained with a concentration of 4 or 
5 grm. of ozone per cubic meter of air treated. Even such a 
yield as that just recorded, is, however, woefully inefficient when 
compared with that theoretically obtainable, for on the basis of 
the energy actually involved in the chemical change from 2 to 
3 , 1 K. W. hour ought to produce approximately 1380 grm. of 
ozone. It will thus be seen that there is still room for consider- 



OZONE: ITS PRODUCTION AND UTILIZATION 109 

able improvement in the production of ozone by electrical means, 
at least in so far as the efficiency of the process is concerned. 

Up to the year 1910 over 100 patents had been issued by the 
United States Patent Office to cover various methods and 
apparatus for the production of ozone, and yet, in spite of this 
fact, this country is considerably behind several of the European 
countries with respect to the development of ozonizing apparatus 
and as regards the utilization of ozone for commercial purposes. 

Most ozonizing apparatus of the present day is similar in 
principle to the ozonizer designed by Berthelot in 1890, a 
diagrammatic sketch of which is shown in Fig. 23. In view of 
the importance of this ozonizer, which served as the prototype 
of the majority of the ozonizers which are now upon the market, 
its construction and the principles of its operation will be briefly 
described. 



To Transformer 



To Ground and 
Transformer - 




Fig. 24. — Siemen's ozone generator. 



The inner glass tube, A, as well as the outer containing vessel, 
B, were filled with dilute sulphuric acid, which is a conductor of 
electricity, and the two wires leading from the static machine 
or transformer made contact with the acid in the tube and that 
in the outer vessel, respectively. Air was forced or drawn 
through the annular space surrounding the inner tube, and was 
thus subjected to the electrical discharge which took place be- 
tween the two concentric glass cylinders. As previously noted, 
both the concentration and the yield obtained with this type of 
ozonizer were extremely low. 



110 [ENGINEERING FOR CENTRAL STATIONS 

Fig. 24 shows the principal features of the Siemen's ozonizer, 
which has achieved a considerable amount of commercial 
success, particularly in Germany. It will be observed that the 
ozonizing element comprises an aluminum cylinder surrounded 
by a glass tube, with an annular space between through which 
the air passes, and across which the electrical discharge is main- 
tained. The outer surfaces of the glass tubes are coated with 
tin foil and are in electrical contact with the metal container, 
which is grounded in addition to being connected to one pole of 
a step-up transformer. The space surrounding the glass tubes 
is filled with water, which serves to keep down the temperature 
in the space between the electrode surfaces. 

In Fig. 25 is shown a cross-section of the Gerard ozonizer, 
which has been used quite extensively in Europe and to a 
limited extent in this country. The ozonizing elements, of 
which there are usually 10 in number grouped in a sheet steel 
tank, consist of concentric glass tubes, with an annular space 
between them across which the electrical discharge takes place. 
The outer tube is closed at its lower end, while the inner tube is 
open and in direct communication with the annular space above 
referred to. All of the inner tubes of such a group of ozonizing 
elements connect with one compartment in the casing which 
surmounts the tank containing the tubes, while all the outer 
tubes connect with another similar compartment in the same 
casing. The air enters one of these compartments, passes down 
through the inner tubes and then up through the annular space 
into the other compartment. In passing upward between the 
tube, the air is subjected to the electrical discharge which takes 
place between the tube surfaces. The inner surfaces of the 
inner tubes and the outer surfaces of the outer tubes are coated 
with tin foil, and these surfaces are connected, respectively, to 
the two terminals of a step-up transformer. The space in the 
tank surrounding the glass tubes is filled with oil, which serves to 
convey the heat away from the tubes to the metal casing of the 
tank. 

The three forms of ozonizers which have been described above 
are all what is known as the "concentric tube" type. In certain 
other makes of ozoniz rs the electrode surfaces are in the form of 
parallel plates, but, generally speaking, the various forms of 
ozonizers are very similar in principle, the differences which 
exist being almost wholly confined to details of construction. 



OZONE: ITS PRODUCTION AND UTILIZATION 111 



Bottom of Tinfoil 
(Outer Tube) 



Bottom of Tinfoil 
(Inner Tube) 



-H— 




Fig. 25. — Cross-section of Gerard ozone generator. 



112 ENGINEERING FOR CENTRAL STATIONS 

One of the largest concerns engaged in the manufacture of 
electrical apparatus in this country has recently placed upon 
the market a small ozonizer — or "ozonator" as it is called — 
designed for effecting the purification and disinfection of air. 
This machine is only one of several that are now available for 
the purpose named, but as it is of very recent design and embodies 
many of the latest features that are to be found in an ozonizer 
of this type, some details will be given concerning its operation. 

The flow of air through this ozonizer is 4000 cu. ft. per hour, 
and the maximum concentration of ozone obtained is 6 mgrm. 
(a milligram being .001 grm.) p r cubic meter of air. The 
consumption of power at maximum ozone output, including 
that required to operate the fan, is approximately 70 watts for 
the A. C. machine and about 87 watts for the D. C. machine, the 
additional power requirements of the latter representing the 
loss incurred in converting the direct current into alternating 
current, which is accomplished by means of a small rotary con- 
verter mounted upon the top of the box which contains the ozon- 
izing apparatus. While the yield of this ozonizer is low (being 
slightly under 10 grm. of ozone per K. W. hour of gross energy 
input, or about 45 grm. per K. W. hour of net energy required 
for ozonizing purposes only), this is of little consequence in view 
of the very small amount of power that is required to purify a 
very considerable volume of air. Under ordinary conditions, 
one of these ozonizers is sufficient for approximately 25,000 cu. 
ft. of space, which means a room of about 40 by 50 ft., with the 
ordinary height of ceiling. As the D. C. machine would consume 
only about 1 K. W. hour of electrical energy if operated con- 
tinuously for 12 hours at maximum output, it will be seen that 
this question of yield is really of very minor importance where 
ozone is being generated for the purification and disinfection of 
air. 

In confining themselves to a brief description of only a few 
makes of ozonizing apparatus, the authors have been obliged 
to pass over, without so much as even mentioning by name, a 
number of other makes which are, perhaps, as well known and 
as successful commercially as those which have been described. 
Mention will be made, however, of one other form of ozonizing 
apparatus, which is quite unique as regards certain features of 
its construction, and which is credited with a yield that is prob- 
ably higher than that given by any other type of ozone generator. 



OZONE: ITS PRODUCTION AND UTILIZATION 113 

The apparatus referred to is that devised by M. Jan Steynis, of 
New York City. 

Perhaps the most striking feature of this ozonizer is the fact 
that the generator itself contains refrigerating coils within which 
the expansion of ammonia gas occurs. These coils were first 
arranged in vertical stands with the lengths of pipe placed 
horizontally and each stand was fitted with a number of vertical 
"straps" which were accurately faced on each side. The faces 
of these "straps" served as electrode surfaces, and they were 
separated by air gaps and dielectric plates. The ammonia 
piping, where it entered the ozonizer, was fitted with insulating 
joints and alternate stands of pipe were connected to the same 
terminal of a step-up transformer. The air passed horizontally 
through the gaps which separated the faces of adjoining "straps," 
and, in so doing, was subjected to a succession of electrical dis- 
charges. The refrigerating coils maintained a uniformly low 
temperature within the generator, and this resulted in very high 
yield of ozone per unit of energy input. By increasing the 
refrigerating plant capacity, this system may be very readily 
extended so as to provide for the pre-drying of the air. While 
the construction of this type of ozonizer has recently been 
changed somewhat from that described above, the refrigerating 
feature remains practically the same. 

The commercial application of ozone which, up to the present 
time, has awakened the greatest amount of public interest and 
which, at the same time, has received the largest measure of 
engineering attention, is unquestionably that of water purifica- 
tion. That drinking water supplies can not only be purified, but 
absolutely sterilized by the means of ozone, is no longer open to 
question. The destruction of the harmful bacteria in water by 
means of ozone is certain, provided the ozone is present in 
sufficient amount and is brought into intimate contact with all 
portions of the water. Whether or not it is practicable to use 
ozone for the purification or sterilization of water is, therefore, 
almost entirely a question of the cost of this method as compared 
with those of other possible methods of securing purification or 
disinfection. 

The most common method of purifying a public water supply 
at the present time is by means of the slow sand-filter — a method 
which involves a considerable investment and which requires a 
large amount of space, if the water to be purified is great in 



114 ENGINEERING FOR CENTRAL STATIONS 

amount. When it comes to the question of the disinfection of 
water — or the complete destruction of all disease-producing 
bacteria — the ozone treatment must compete with the use of 
hypochlorite of lime or soda and with a still newer process which 
involves the use of ultra-violet rays produced by means of the 
mercury arc in a quartz tube. While the hypochlorite treat- 
ment has proven very effective, and while its cost is insignificant 
as compared with other methods, it involves the addition of a 
chemical substance to the water, which is generally looked upon 
with disfavor by the public at large. On the other hand, the use 
of ozone or the ultra-violet rays for the disinfection of water is 
almost certain to appeal quite strongly to the public imagination. 
In a recent test where some badly polluted water was treated 
with ultra-violet rays, practically the complete sterilization of 
the water was brought about with an energy consumption of 26 
watt hours per cubic meter of water treated, which is equivalent 
to about 100 K. W. hours per million U. S. gallons. It will be 
of interest to compare this figure with those which are given below 
in connection with ozone when employed for this purpose. 

About the first attempt to utilize ozone for the purification of 
water on a commercial scale was that made by Tindal in Paris in 
1895. An experimental plant was erected at St. Maur, Paris, on 
the River Marne. This plant has undergone since that time a 
number of changes and its capacity has been considerably 
increased. Tests made upon this plant in 1908 showed a con- 
sumption of 47.5 K. W. hours per million U. S. gallons for the 
production of ozone and 63.4 K. W. hours per million gallons for 
pumping purposes. Several other water purification plants, in 
which no pumping is required, show an average energy consump- 
tion of about 80 K. W. hours per million U. S. gallons, while an 
experimental plant that was erected in New York City in 1906 
is stated to have required a consumption of 800 K. W. hours per 
million gallons of water treated, of which only 25 per cent, was 
required for the generation of ozone, the balance being expended 
in pumping the water and in blowing and cooling the air. It 
will be seen from these figures that the consumption of electrical 
energy varies widely, but this is only what is to be expected 
when consideration is given to the fact that the character of the 
water undergoing treatment, as well as the efficiency of the proc- 
ess by which the ozone is produced, may be radically different 
in one plant from what it is in another, and that the method 



OZONE: ITS PRODUCTION AND UTILIZATION 115 

followed in applying the ozone to the water may affect the results 
secured to a very considerable extent. 

The use of ozone affords a simple and inexpensive means of 
destroying any harmful bacteria that may be present in water 
from which ice is to be made, particularly in the case of "plate" 
ice plants, which ordinarily use raw, or undistilled, water. 
Several such ice plants are now using ozone for this purpose. 
In one particular "plate" ice plant, ozone is being produced by 
means of electrical energy generated by a motor-generator set 
of 2 1/2 H. P. capacity, the potential being raised by means of a 
transformer to 14,000 volts for use in the ozonizer. It is stated 
that the practically complete sterilization of the water used in 
this plant is secured with an energy consumption of 3 K. W. 
hours for each 50 tons of ice produced. 

While some reference has been made above to the use of ozone 
in connection with ventilation, this phase of the subject is of 
sufficient importance to warrant a much more extended treat- 
ment than is possible within the limits of this chapter. Suffice it 
to say that this field for the utilization of ozone has as yet hardly 
been entered upon, but it is already replete with possibilities. 
Not only does ozone afford a means of greatly improving the 
condition of the air in our dwellings and in our places of business 
and amusement, but by means of this gas it is now possible to 
purify and largely free of smoke and fumes the air of those places 
where certain industrial processes are carried on, and where 
ordinary methods of ventilation have largely failed. The puri- 
fication of the air in work-rooms and factories is not only of 
hygienic but of economic importance, and no employer of labor 
should be willing to incur the loss in human efficiency which must 
invariably accompany the impairment of the vigor and activity — ■ 
both mental and physical — of those workmen and workwomen 
who are subjected to the deadening effects of bad air. 

The sterilizing and disinfecting properties possessed by 
ozonized air, together with the fact that, while very destructive 
to the lower forms of animal and vegetable life, it is harmless so 
far as human beings are concerned, except in very high concen- 
trations, points to the probability of ozone becoming of great 
value in connection with therapeutic and surgical work. As a 
matter of fact, ozone has already been used for sterilizing rooms, 
bandages and surgical instruments in a number of hospitals, 
with a high degree of success. Ozonized air has already entered 



116 ENGINEERING FOR CENTRAL STATIONS 

the field of medicine, where it has been applied locally in the case 
of various skin diseases and cancerous growths; and it is also 
claimed that the inhalation of ozonized air, when mollified by 
the presence of certain oily vapors, has proven very successful in 
cases of pulmonary trouble. 

Ozone has already been employed experimentally with con- 
siderable success as a preservative of food products, such as 
eggs, fruits, meat and other produce of a perishable nature. Its 
use in this connection is proposed as an auxiliary to cold-storage, 
and it is believed that a material reductio 1 will thereby be made 
in the amount of refrigeration required. It has been found that 
the growth of various forms of molds and fungi and those forms 
of decay which originate on the surfaces of meats and other food 
products, can be effectively prevented by means of ozonized air. 

In the manufacture of wines and liquors ozone has been used 
very successfully for sterilizing vaults and casks, and it is claimed 
that it affords a very satisfactory means of effecting the artificial 
"ageing" of wines. A very important field for the use of ozone 
is to be found in the bleaching of flour, sugar, starch, woolen and 
cotton goods, feathers, oils, etc. While the use of ozone may be 
slightly more expensive than the use of calcium hypochlorite 
for textile bleaching, the superior mechanical condition of the 
goods after bleaching with ozone will doubtless make the use of 
this agent commercially preferable. Another important field 
for the use of ozone is to be found in the treatment of oils, greases, 
tallows, etc., inasmuch as ozonized air affords a means of pre- 
venting the rancidity of, and of destroying the offensive odors 
given off by, such products while undergoing manufacture. 

While the foregoing list of the industrial uses to which ozone 
has already been applied, or for which it has been proposed, is 
by no means complete, it will, perhaps, serve to convey some idea 
of the present and, more particularly, of the probable future 
commercial importance of this gas. 



CHAPTER XI 

THE USE OF ELECTRICITY FOR THE DISINFECTION OF SEWAGE 
INTRODUCTORY 

The satisfactory disposal of sewage is a problem that is 
becoming more and more serious as our urban populations 
increase and as our sanitary standards advance Even some of 
our seaboard cities, with immense quantities of tidal waters at 
their doors, are experiencing more or less difficulty in effecting; 
the satisfact ry elimination of their constantly increasing 
quantities of refuse matter. Cases in point are to be observed 
in the agitation which has recently arisen in connection with 
the proposed discharge of Passaic Valley sewage into New York 
Bay, with the increase in harbor pollution which, it is feared, 
would result therefrom; also in the case of Baltimore, where a 
very elaborate system of sewage purification has been under- 
taken to overcome the serious pollution of the Patapsco River. 
In order to provide against the further pollution of Lake Michi- 
gan, from which the City of Chicago secures its water supply, it 
was necessary to construct a canal, at a cost of nearly forty 
million dollars, for the purpose of diverting the sewage of Chicago 
into the DesPlaines River, which flows towards the southwest 
and empties into the Illinois River, the latter discharging into 
the Mississippi. 

Those towns and cities which have no tidal waters or large 
rivers at hand for the disposal of their sewage by dilution, have 
been obliged to resort to various methods of artificial purification, 
such as the use of sewage farms, otherwise known as "broad 
irrigation," intermittent sand-filters, trickling filters, contact- 
beds, etc. While the intermittent filtration of sewage through 
sand is usually quite effective as regards the removal of bacteria, 
this cannot be said of the more rapid methods of sewage purifica- 
tion which are in quite general use to-day. The tendency of 
late years has been to increase the rate at which sewage can be 
treated upon a given area of land, and this has resulted in the 
development of the contact bed and the trickling filter, the latter 
frequently requiring only an area of surface to each 2 or 3 

117 



118 ENGINEERING FOR CENTRAL STATIONS 

million gallons of sewage handled per day. While the amount of 
land required for handling a given amount of sewage has thus 
been greatly reduced, the resulting bacterial purification has, as 
a consequence, been very materially lessened. 

At the present time there seems to be no very definite under- 
standing as to the exact nature of the responsibility which rests 
upon a community as regards the condition of its discharged 
sewage, even where the water supply of some other community 
is directly endangered thereby. Court decisions, however, have 
quite firmly established the principle that both injunctions and 
damages may be obtained by riparian owners when sewage is 
discharged into a stream in such quantities as to markedly alter 
its characteristics. 

With increasing sanitary knowledge, it would appear that the 
day is not far distant when public sentiment — doubtless crystal- 
lized into the form of laws — will demand a very considerable 
degree of bacterial purity in the sewage of any community when 
such sewage is so discharged as to be a possible source of contami- 
nation to the water supply of any other community. An enlight- 
ened public opinion will also doubtless insist upon the absence of 
pathogenic germs in sewage which has access to shellfish beds, 
either by prohibiting the location of such beds within the waters 
adjacent to large cities, or, where the shellfish industry is of 
sufficient importance, by requiring the disinfection of all sewage 
which threatens contamination to such beds. When the City of 
Baltimore recently determined to discharge all of its sewage at 
a single point into Chesapeake Bay, the oyster industry of that 
section quite naturally became alarmed. In order to afford 
protecton to this important industry, the Sewerage Commission 
of Baltimore finally specified "that the effluent proposed to be 
discharged into Chesapeake Bay or its tributaries in the system 
to be recommended by the engineers shall be of the highest 
practicable degree of purity." 

To give some idea of the importance of the shellfish- industry, 
it may be stated that the annual crop of oysters gathered along 
the Atlantic and Gulf coasts in 1902 amounted to over 25 million 
bushels, having a value of over $13,000,000, and that the crop of 
clams was in excess of 2 million bushels with a value of some 
$2,000,000. Of this total output over one-half came from the 
waters adjacent to the states of Virginia, Maryland and New 
Jersey, and for the most part from the waters of Chesapeake and 



DISINFECTION OF SEWAGE 119 

Delaware Bays, which serve as outlets for the sewage of a number 
of large cities. It will thus be seen that the importance of the 
shellfish industry in many localities is such that the disinfection 
of all sewage, having even remote access to the shellfish beds, 
becomes imperative, and it is not reasonable to believe that the 
public will much longer tolerate the dangerous possibilities which 
lurk in the marketing of shellfish that are grown in waters into 
which infected sewage is being discharged. 

The need for disinfecting sewage, is, therefore, primarily con- 
fined to those cases where shellfish beds of considerable value are 
threatened (it being assumed that, where the investment in 
shellfish beds is inconsiderable in amount, it would be cheaper 
for a city or town to remove this industry through purchase 
rather than to incur the expense of sewage disinfection) and where 
the possible pollution of water supplies exists. Under certain 
circumstances, it may be necessary also to purify sewage bac- 
terially before it is discharged into a body of water which is used 
extensively for bathing purposes. Moreover, sewage which is 
infected to an unusual degree, such as that from a contagious 
disease hospital, should, without doubt, be required to be disin- 
fected in all cases, irrespective of the manner in which such sew- 
age may finally be disposed of. 

Having thus outlined very briefly the general conditions under 
which the disinfection of sewage becomes either necessary or 
desirable, we will next consider the more important methods 
and substances which have either been proposed or tried in this 
connection, and in this way lead up to the use of electricity for 
this purpose. 

The use of electricity in connection with the disinfection of 
sewage is by no means new. This subject awakened a consider- 
able amount of interest in the early nineties, and since then it 
has received, at intervals, more or less attention at the hands of 
electrical and sanitary engineers. The claim is frequently made 
that, in the disinfection of sewage and in the purification of 
municipal water supplies, there exists a promising field for 
central station service. This article will only deal with the 
former of these two subjects, and, after a brief historical review 
of the use of electricity in this connection, an attempt will be 
made to analyze the possibilities which appear to reside in sewage 
disinfection from a central station point of view. 

The following substances and methods are believed to include 



120 ENGINEERING FOR CENTRAL STATIONS 

all of the more important of those which have been tried or pro- 
posed in connection with the disinfection of sewage: 

(1) Heat; (2) lime; (3) acids; (4) copper sulphate; (5) oxidizing 
agents, including ozone, permanganates and those compounds 
which yield chlorine. 

Heat. — The use of heat, by means of a patented process, was 
suggested by Klein (Report of the Royal Sewage Commission, 
1901), the idea being that sufficient ammonia could be obtained 
from the sewage to almost pay for the cost of the treatment. 
Prof. E. B. Phelps (Water-supply Paper 229, U. S. Geological 
Survey) estimates that the cost of fuel necessary to treat one 
million gallons of Boston sewage by this method would be $7, 
and that the market value of the recovered sulphate of ammonia 
would be $20, but " whether the difference between the value of 
the ammonium sulphate and the cost of the fuel is sufficient to 
cover the cost of operation, including labor, evaporation of the 
dilute solution, and all fixed charges, can be determined only 
by actual experiment, but the plan is not wholly without 
possibilities." 

Lime. — While caustic lime is a valuable percipitating agent 
when used for the purification of sewage by means of chemical 
precipitation, and in this r61e is successful in removing a large 
number of bacteria, it is not an efficient bactericide. Rideal 
found that one part of lime to one thousand parts of sewage 
failed to produce satisfactory bacterial purification. 

Acids. — It has been found that acids, as a general rule, have a 
more destructive effect upon bacteria, especially upon the patho- 
genic germs, than the alkalies. While acids have been employed 
for sewage disinfection, the cost of the treatment has been found 
to be excessive, largely due to the fact that free alkali is usually 
present in sewage in considerable amount, and this must be 
neutralized before the germicidal action of the acid becomes 
effective. 

Copper Sulphate. — Copper sulphate, as a sterilizing agent for 
bot water and sewage, has received a considerable amount of 
attention at the hands of investigators in this country. Probably 
the most extensive tests which have been made with this com- 
pound are those of Kellerman, Pratt and Kimberly, which were 
carried on in Ohio during the winter of 1906-7. As a result of 
these tests, the investigators reached the conclusion that copper 
sulphate was not as efficient a disinfectant as the chloiine com- 



DISINFECTION OF SEWAGE 121 

pounds, that it was more seriously affected by carbonates, and 
that it was considerably more expensive. 

Oxidizing Agents. — While ozone has been employed to some 
extent for sterilizing water during the past few years, and while 
the future would appear to hold out considerable promise of a 
more extended use for it in this connection, it does not look as if 
ozone would find any considerable field of usefulness in the dis- 
infection of sewage. Even if the cost of generating ozone be- 
comes materially less than what it is at present, its slight solubil- 
ity in water will still serve as a handicap to prevent its use in 
treating sewage which contains any considerable amount of 
solid matter, inasmuch as the rate at which a dissolved gas 
penetrates solids in a liquid is a direct function of the solubility 
of the gas. 

Permanganates yield nascent oxygen in both acid and alkaline 
solutions, and both potassium permanganate and sodium 
permanganate have been employed for oxidizing organic matter 
in streams. The latter has been used for treating the water of 
the River Thames at London, during pe: iods of low water, for 
the purpose of destroying odors and putrescible matter. Dibdin 
found it preferable to chlorine for this purpose, as the sewage, 
after having been partially sterilized by chlorine, underwent a 
subsequent putrefaction which was particularly offensive. This 
was thought to be due to the partial destruction of the nitrifying 
organisms, which were not destroyed to any such extent when 
permanganate was used. 

In chlorine and in some of its compounds we have, undoubt- 
edly, the most efficient and the cheapest disinfecting agents that 
are at present available. Chlorine gas has long been known as 
a powerful germicide and as an efficient bleaching agent. In 
this latter capacity, it acts upon organic coloring matter in- 
directly by combining with the hydrogen in the water in which 
it is dissolved, thereby freeing nascent oxygen, by which the 
organic matter is attacked. Its germicidal action is similar, 
and likewise depends upon the liberation of nascent oxygen. 
While chlorine was formerly manufactured commercially by 
chemical methods solely, and is still so made in Europe to some 
extent, electrolytic processes have now largely replaced these 
older methods and have brought about a considerable reduction 
in the cost of manufacture. Chlorine gas is handled with some 
difficulty and danger, but chlorine in the form of a hypochlorite 



122 ENGINEERING FOR CENTRAL STATIONS 

is not only convenient to use, but it has been found to be more 
efficient in disinfection work than when it is supplied in the gase- 
ous form. 

The principal commercial form of chlorine at present is chloride 
of lime, or bleaching powder, which consists for the most part of 
calcium hypochlorite and contains some 35 to 40 per cent, of 
available chlorine. This bleaching powder is made in large 
quantities in this country, notably at Niagara Falls, by passing 
chlorine, obtained by the electrolysis of salt, over freshly-slaked 
lime. A somewhat higher cost of production, together with 
some difficulty in preparing and keeping them in a dry state, has 
limited the commercial use of the hypochlorites of sodium and 
magnesium. Calcium hypochlorite has long been known as a 
powerful and efficient disinfectant, and has been extensively 
used for disinfecting purposes. It was used for deodorizing 
London sewage as early as 1854, while in 1885 a Committee of 
the American Public Health Association reported it to be the 
best and most efficient disinfectant then available. Many 
investigations of the use of bleaching powder for the purpose of 
sewage disinfection have been made, notably in Germany, 
India and, more recently, in this country. In the German tests 
crude sewage was dealt with, and a seemingly unnecessarily high 
degree of bacterial purity was demanded. Under these circum- 
stances large quantities of chlorine were required, and the cost 
of the process was, in consequence, high. The American tests, 
however, have been very favorable to the use of chloride of lime, 
and the results obtained in these tests will be referred to later on 
in this chapter. 

HISTORICAL 

The Webster Process. — The first recorded application of 
electricity to the treatment of sewage was the process devised 
by Mr. William Webster, of London, over 20 years ago. The 
first practical demonstration of this process, on a working scale, 
was carried out at the main drainage outfall at Crossness, near 
London, early in the year 1889, where a sewage flow of 12,000 
gallons per hour was dealt with. At the outset, the Webster 
process was really one of chemical precipitation, rather than one 
of chemical disinfection secured through electrolytic means. 
The sewage was forced to flow through channels or weirs in 
which iron electrodes were suspended from cross-bars. As the 



DISINFECTION OF SEWAGE 123 

sewage traveled along these channels, every portion of the liquid 
was subjected to the action of the electric current, and precipita- 
tion of the solid parts in the sewage took place. The sewage was 
then passed through settling tanks, after which it was discharged 
in what was claimed to be a purified condition into the River 
Thames. In the plant in question the electromotive force 
emploj^ed was only a little over two volts, and a very low current 
density was used, there being some 11 sq. ft. of iron electrode 
surface per ampere. While this process, as stated above, 
was originally one of purification by means of chemical precipita- 
tion, Mr. Webster early recognized the value of the hypochlorites, 
which resulted from the electrolytic action, as active disinfecting 
agents. 

The precipitating action was due to the formation of salts of 
iron, the chlorine and oxygen liberated in the electrolysis of the 
sewage first acting upon the positive iron electrode with the 
formation of hypochlorite, which was afterward decomposed by 
the alkalies which were present at the negative electrode, with 
the formation of insoluble salts of iron, and these salts, in settling 
to the bottom, effected the removal of a large part of the in- 
soluble organic matter in the sewage. The presence of iron in 
solution at the positive pole made it possible to carry on the 
action at a lower voltage than that which is required to liberate 
free chlorine from an alkali chloride solution. 

In describing the oxidizing action which resulted from this 
electrolytic treatment, Mr. Webster stated that the chemical 
changes which took place in the sewage when electrolyzed de- 
pended chiefly upon the well-known action of sodium, magnesium 
and other chlorides (which are always present in sewage) when 
split up into their constituent parts, and that the chlorine and 
oxygen which were liberated at the positive pole in a nascent 
state were intensely active and rapidly oxidized the organic 
matter in the sewage into innocuous compounds. He further 
stated that the hypochlorite which was formed absolutely de- 
stroyed all organic matter, living or dead. A little later Mr. 
Webster devised a form of electric filter — one form consisting of 
layers of coke separated by layers of sand, the beds of 
coke alternately forming positive and negative electrodes— 
which, when used in conjunction with the iron plate treatment 
above described, was claimed to produce any degree of purity in 
the sewage which might be required. 



124 ENGINEERING FOR CENTRAL STATIONS 

While the Webster process was undoubtedly effective in pro- 
ducing a stable and partially purified effluent, the cost of the 
treatment was excessive, and the bacterial purfication was 
probably not sufficiently complete to warrant the use of the proc- 
ess where the destruction of pathogenic bacteria was the main 
object sought. While this process was tried experimentally in 
one or two other places, it never became a practical success, 
principally for the reasons above noted. However, it became the 
forerunner of several somewhat similar processes which received 
more extended trials and which attracted a greater amount of 
attention. 

The Woolf Process.— Under date of March 22, 1892, a United 
States patent was issued to Mr. A. E Woolf of New York City, 
for a process of producing hypochlorite of sodium, etc., by 
electrolysis. The cathodes were described as parallel perforated 
plates of carbon, between which a platinum anode was placed. 
The electrolyzed solution which was obtained was given the trade 
name of "electrozone." 

The Department of Health of New York City soon made an 
investigation of the disinfectant properties of this solution, and in 
a report made by Dr. E. W. Martin, who was at that time Chemist 
to the department of Health, to Dr. Cyrus Edson, then Sanitary 
Superintendent of New York, the action of this disinfectant was 
thus described: 

"Part of the chlorine in the hypochlorite replaces a part or the 
whole of the hydrogen in the organic substances; another portion 
unites with the liberated hydrogen, and, as in bleaching, ozone 
is produced, which in its turn, acts on the organic matter. In 
other words, the organic matter, be it organized as in the lower 
forms of vegetable life, or non-organized as in the solid or sus- 
pended matter of sewage, is decomposed, and if sufficient hypo- 
chlorite be present the organic matter is permanently disinfected. 
In my opinion the solution in question will prove an absolute 
disinfectant, if applied in sufficient quantities to organic matter 
either of animal or vegetable origin." 

Doubtless as a result of this investigation by the Department 
of Health, a plant was ordered by the New York Department of 
Public Works and was installed at Brewsters, N. Y., in the sum- 
mer of 1893. This plant was used for the purpose of disinfecting 
the sewage of some 30 dwellings which were located in the 
Croton watershed. The plant consisted of a boiler, an engine, 



DISINFECTION OF SEWAGE 125 

and a dynamo, the latter delivering some 700 amperes at a 
potential difference of 5 volts. Common salt was added to the 
water at the rate of 160 lb. per 1000 gallons, and in the tank 
containing this brine two electrodes were located, the positive 
electrode being made of copper plated with aluminum, while 
the negative electrode was made of carbon. The electrolyzed 
solution flowed from this tank into the sewer outlet at the rate of 
1 gallon per 1000 gallons of sewage, and the disinfected sewage 
was then discharged into a trench some 200 ft. long, to which 
four laterals, some 75 ft. long, were excavated at right angles. 
From these trenches the sewage filtered through the earth to a 
neighboring brook, which drained eventually into the Croton 
reservoir. 

The operation of this plant was considered a success, both 
from a bacteriological and from a financial point of view. Tests 
showed that the electrolyzed solution was an efficient germicide, 
and that the cost of operation, when compared with the cost 
when other forms of disinfectants were used, was low. With 
salt at $4 per ton, the cost of the salt required to treat one million 
gallons of sewage was $3.20, to which, of course, must be added 
the cost of coal, labor, water, etc., together with the fixed charges 
upon the plant investment. However, as compared with the 
price of other forms of disinfectants, it was claimed that the 
electrolyzed solution showed a considerable saving. 

This plant was shortly afterward enlarged for the purpose of 
purifying with "electrozone" the water in a brook which con- 
nected the Sodom storage reservoir with the Croton reservoir. 
A 2 or 3 per cent, solution of salt and water, after electrical 
treatment, was discharged into this stream at the rate of about 
10 gr. to a gallon of water (one part in 5282), which was 
equivalent to some 43 lb. of salt per million gallons of water 
treated. This water treatment was, however, soon abandoned, 
but the sewage disinfecting plant is still in operation. 

This Woolf process was shortly afterward made use of in the 
vicinity of New York City for a purpose other than sewage dis- 
infection, although somewhat analogous in character. Riker's 
Island, located in the East River, was at that time used as a 
dumping ground for a considerable portion of New York City's 
garbage. An intolerable condition soon arose, for this putrifying 
mass of several acres in extent soon became extremely offensive, 
not only to persons who were obliged to pass near the Island in 



126 ENGINEERING FOR CENTRAL STATIONS 

boats, but to those who resided in the nearby sections of New 
York City and Long Island. It became imperative that some 
action should be taken to stop this nuisance, so in the summer of 
1894 an " electrozone " plant was installed upon a barge which 
was towed to Riker's Island, and the salt water of the East River 
was converted into a disinfecting fluid which was pumped through 
lines of hose and sprayed upon the decomposing mass of garbage. 
As a result of this treatment, the obnoxious odors were very 
greatly reduced and were confined to an area of comparatively 
limited extent. 

The first city to adopt the Woolf process for the purification 
of its sewage was Danbury, Conn., where a plant was installed 
in 1894. The population of this city at that time was something 
over 16,000, and a plant was installed which consisted of an 
engine and a dynamo, the latter furnishing a current of 1000 
amperes at about five volts. The "electrozone" was generated 
in a tank located above another tank through which the sewage 
flowed, and the disinfectant and sewage were thoroughly mixed 
in the latter by means of an agitator. From this mixing tank 
the sewage flowed through a line of pipe and discharged into a 
neighboring stream. The cost of operating this plant was stated 
to be about $12.50 per day — $7.50 for labor and $5 for salt, oil 
and fuel — which was equivalent to approximately 27 cents per 
year per capita of population. 

The operation of this plant was not a success, although the 
analytical results that were secured were considered to be good. 
The chief trouble arose from the fact that the heavy part of the 
sewage was not only not removed, but was only acted upon by 
the disinfectant so far as its outer surfaces were concerned, thus 
leaving the inner portions in a practically unchanged condition. 
As a result of this, property owners along the stream into which 
the sewage was discharged brought law suits against the city on 
the ground that the solid matter in the sewage filled up their 
mill ponds. This difficulty might possibly have been overcome 
by passing the sewage through screens and settling tanks before 
it was subjected to the disinfecting process, but, after a consider- 
able amount of litigation, the city was forced to abandon the 
process entirely and to substitute intermittent sand filters for 
treating its sewage. 

An "electrozone" plant was installed by the public authorities 
of Philadelphia in 1895, and the hypochlorite solution was used 



DISINFECTION OF SEWAGE 127 

by the Health Department for disinfecting dwellings after con- 
tagious diseases. This plant continued in operation, more or 
less continuously, for a number of years, but it was finally 
abandoned in 1906. A plant was also installed in 1893 at the 
Foot of Canal St., New York City, and the "electrozone" was 
employed for disinfecting the sewage polluted water surrounding 
the pier of the Albany Day Line. This plant, however, was only 
continued in operation for a comparatively short time. 

Perhaps the most notable application of the so-called Woolf 
process for disinfecting purposes was its use in connection with 
the cleansing of Havana, Cuba, which took place when the 
American authorities succeeded the Spanish early in the year 
1899. In view of the extraordinarily bad conditions which had 
to be met, it was recognized that ordinary methods would not 
serve, and as electrolyzed salt water was then much in evidence 
as an effective disinfecting agent, it was decided to install an 
" electrozone" plant. After some preliminary experiments, a 
plant consisting of four 100 K. W. dynamos was installed. There 
were eight electrolyzing vats into which sea water was pumped 
from the bay. In each vat there were 417 positive electrodes 
consisting of an alloy of platinum and iridium, and 425 negative 
electrodes which were made of zinc. Two vats were operated in 
series, 6 volts being required per vat. The sewers and unpaved 
portions of Havana were treated with the electrolyzed solution, 
and the results which were obtained were viewed as being highly 
satisfactory. This treatment, doubtless assisted by other 
sanitary measures, was instrumental in very greatly reducing 
the number of deaths resulting from yellow fever. 

The Woolf process was introduced into England in 1895 and 
an experimental plant for the treatment of sewage was erected 
at Maiden Head in the year 1896. While the trials carried on at 
this plant attracted a considerable amount of attention, and 
while the results obtained were satisfactory from a bacteriological 
point of view, the process was finally abandoned on account of 
its high cost, and the company which financed the process 
ultimately went into liquidation. The " electrozone" process 
was later carried on under the Crawford patents instead of the 
Woolf, and in 1906 " electrozone" was being manufactured in 
England and being distributed in bottles as a stable form of 
disinfectant for domestic and hospital use. 

The Hermite Process. — The Hermite process was very similar 



128 ENGINEERING FOR CENTRAL STATIONS 

to the so-called Woolf process which has just been described. A 
United States patent was issued to Eugene Hermite of Paris, 
France, under date of March 4, 1884, and this patent covered the 
production of a bleaching and disinfecting fluid by means of the 
electrolysis of an alkali chloride, especially sea salt, in a dia- 
phragm cell containing electrodes of lead, with the formation of 
caustic and lead chloride. The lead chloride was then mixed 
with water and a small quantity of hydrochloric acid and the 
mixture was subjected to electrolysis in the presence of the tex- 
tile fabrics which were to be bleached. Further United States 
patents were granted to Hermite in the years 1888 and 1889, 
and they covered the production of magnesium hypochlorite for 
bleaching purposes by the electrolysis of magnesium chloride, 
using anodes of platinum, held rigidly in place, between which 
zinc cathodes, in the form of discs mounted upon a horizontal 
shaft, revolved. Scrapers were provided to remove the deposited 
magnesium hydrate from the cathode surfaces. 

In the early stages of the Hermite process considerable stress 
was laid upon the superiority of magnesium hypochlorite to the 
other hypochlorites as a bleaching and disinfecting agent, but 
as a result of the deposition of the magnesium hydrate upon the 
zinc discs, which the scrapers did not satisfactorily remove, and 
which resulted in a considerable increase in the electromotive 
force required to carry on the process, the use of a solution of 
magnesium chloride as an electrolyte was finally discontinued, 
and a sodium chloride solution was used in its place, although a 
small quantity of magnesium chloride was sometimes added to 
the solution. 

The Hermite process was tried at Rouen, France, for disinfect- 
ing purposes as early as 1889. Experimental plants were after- 
ward installed at Havre, Paris, Marseilles, Brest, Nice, Loriente 
and Bombay, and at Lytham, Worthing, Ipswich and South 
Hampton in England. 

The method first proposed for applying the Hermite disin- 
fectant was radicaly different from that followed in the Woolf 
process, as exemplified in the cases of Brewsters, N. Y., and 
Danbury, Conn. With the Hermite process the idea was to 
disinfect the sewage at its source, rather than to treat it as a 
whole just before its final disposal. This plan called for a main 
generating station, pumps for circulating the fluid and a system 
of distributing mains with a connection leading to each house 



DISINFECTION OF SEWAGE 129 

for the purpose of flushing each toilet and sink. Such a system 
was thought to be necessary, as in the majority of European 
cities and towns the sewage systems were of the combined type, 
in which both the household wastes and the storm waters were 
admitted. It was at first believed that, were the fluid applied 
to the sewers directly, it would be so diluted by the storm waters 
that the effectiveness of the treatment would be largely de- 
stroyed. As the cost of such a system was considerable, to say 
nothing of its complication, the majority of the cities and towns 
which made a trial of the Hermite system used the disinfecting 
fluid for flushing the sewers only. 

At Ipswich, England, a Hermite plant was installed in 1895 
for the purpose of disinfecting a main sewer which emptied into 
a river by which the city is divided, the purpose being to prevent 
the decomposition of the sewage until it was carried well out to 
sea. This plant is stated to have cost $12,000, and consisted of 
a 30 H. P. engine, a dynamo capable of delivering 600 amperes 
at 28 volts and four electrolyzers connected in series. The 
electrolyzers were of sufficient capacity to yield 1 grm. of 
chlorine per capita of population in 24 hours. This plant was 
continued in operation until 1905, when it was abandoned on the 
ground that the results obtained did not warrant the expenditure. 

At Brest, the experiments with the Hermite process were 
carried out on quite an extensive scale, the sewage from 11,000 
people being treated. In an official report upon this plant, 
made in 1894, it was stated that " electrolyzed water is a perfect 
disinfectant and an excellent antiseptic which very rapidly 
destroys all microbes, even the most tenacious of life, on the 
condition that these microbes are brought into contact with the 
electrolyzed sea water." 

An experimental plant was installed at Havre in 1893, con- 
sisting of two 35 H. P. engines with double electrolyzers, five 
centrifugal pumps, three of which were used for forcing the dis- 
infectant into an elevated tank, while the remaining two were 
used for conveying a supply of sea water and for circulating the 
liquid through the electrolyzers. The experiments at this 
plant showed that 440 gallons of disinfecting fluid, containing 
approximately 35 gr. of chlorine per gallon, could be pro- 
duced per hour at a cost of $13.30 per day. These plants were 
investigated by a commission appointed by the Council of 
Hygiene of Paris and also by a German commission appointed by 

9 



130 ENGINEERING FOR CENTRAL STATIONS 

the Imperial Board of Health, but both of these bodies made 
adverse reports. 

So far as the authors know, all of the experimental Hermite 
plants that were installed in the early nineties were sooner or 
later abandoned, and for reasons which were practically identical 
with those which caused the Woolf process to be unsuccessful for 
purposes of sewage disinfection at D anbury, Conn. The prin- 
cipal objection to both of these processes was apparently the 
fact that the deodorizing fluid was unable to penetrate the solid 
portions of the sewage. The outer surfaces of these solid portions 
were sterilized, but the inner portions were left to undergo 
decomposition and to breed disease germs. The Hermite 
process was more successful when applied simply for the purpose 
of lessening the effluvia from main sewers and for retarding 
decomposition, as in the case of Ipswich. 

It is of interest at this point to quote the views of Col. George 
E. Waring, Jr. upon the question of sewage disinfection, as 
presented in his book, entitled "Modern Methods of Sewage 
Disposal, " which was published in 1903: 

"Latterly a new process of sterilization by the action of chlorine com- 
pounds, produced by the electrolysis of salt (as in sea water) has attracted 
some attention in New York under the name of the Woolf process and in 
France under the name of the Hermite process. The sterilizing agents thus 
produced have practically the same chemical constituents as ' bleaching 
powder,' and similar results will be obtained by the use of the latter. But 
the apparent novelty of the process, the popular fascination of electrical 
methods and the name ' electrozone' given to these agents, have appealed to 
the fancy of the public and results are hoped for beyond the expectation of 
those who understand the true conditions and difficulties of purification on 
a large scale. The objection to ' electrozone' and all other disinfecting com- 
pounds is that, in so far as they are effective, they are pernicious. What 
we have to do is to infect our sewage as quickly and as completely as pos- 
sible and make it as fertile as possible for the growth of bacteria. In other 
words we must not 'pickle' it; we must favor its quick decomposition. 
Decomposition is inevitable, and the earlier it is completed, the better." 

The opinion which Col. Waring held concerning the disinfection 
of sewage, was, and is, undoubtedly the correct one so far as 
the general question of sewage purification :s concerned, and any 
sterilizing process, if adopted for the purpose of changing the 
putrescible matter in sewage at once into harmless and useful 
compounds, is doomed to as great a failure now as when attempted 
bv Webster, Hermite or Woolf. Putrescible matter must un- 



DISINFECTION OF SEWAGE 131 

dergo putrefaction before it can be reduced to an inorganic state, 
and as bacteria play a most important part in this reducing proc- 
ess, it is evident that the sterilization of sewage only delays this 
putrefactive process. This fact was recognized in later sewage 
disinfecting experiments, in which the disinfecting treatment was 
supplementary to some method of sewage purification, the idea 
being to secure a reasonably high removal of the pathogenic 
germs, without excessive destruction of the beneficient bacteria. 

In 1906, under the advice and direction of Dr. Alexander, 
Medical Officer of Health of the Borough of Poplar, London, a 
plant, making use of the Hermite process in a slightly modified 
form, was installed by the public health authorities for the pur- 
pose of producing, electrolytically, a hypochlorite solution for 
general disinfecting purposes. While this plant is not directly 
employed for the disinfection of sewage, it is worth commenting 
upon in this connection in view of the reported success which has 
attended its operation. 

The borough in question comprises one of the poorest and most 
thickly-populated sections of London, and, in consequence, 
unusual precautions are necessary to maintain the proper 
standards of sanitation. The solution which is electrolyzed is 
a mixture of magnesium chloride and sodium chloride, and during 
the electrolytic process this solution flows consecutively through 
some 40 cells, which are connected in series electrically across 
approximately 240 volts. The positive electrodes are made 
of thin plantinum wire wound upon slate slabs, while the nega- 
tive electrodes are made of zinc. 

During the first 2 years of this plant's operation over 
32,000 gallons of this disinfecting solution were produced at a 
total cost for materials and electricity (purchased as a rate of 3 
cents per kilowatt hour) of approximately $300, which is a trifle 
under 1 cent per gallon. The strength of the solution ranged 
from 4 to 5 grm. of available chlorine per liter. This solution 
has been very successfully used by the health authorities in disin- 
fecting the public buildings; also, when diluted largely by water, 
for flushing the streets and other public places, for which pur- 
pose it is sold to the department which has the care of the streets 
in its charge, at the rate of 2 cents per gallon. When compared 
with the cost of using carbolic acid and similar forms of disin- 
fectants this electrolyzed solution is stated to have shown a large 
yearly saving. 



132 ENGINEERING FOR CENTRAL STATIONS 

The Oxychloride Process. — The so-called oxychloride process, 
as developed in England by a company incorporated under the 
name of "Oxychlorides, Limited/' is very similar in principle to 
the Woolf and Hermite processes above described. Practically 
the only difference is one of detail in the construction of the 
electrolytic cell, for which a higher efficiency in the production of 
hypochlorites is claimed. The type of cell used in this process 
is covered by an English patent issued to George J. Atkins, of 
London, in 1901, and by an United States patent issued in the 
following year. The latter patent describes this electrolytic cell 
as a trough-like vessel of wood lined with carbon, which serves 
as an anode, within which a horizontal, cylindrical cathode of 
wood, covered with lead, revolves. The electric connection of 
the cathode comprises a copper ring with a rubbing contact 
block, and a scraper of rubber or felt was designed to bear on the 
revolving cathode for the purpose of removing the hydrogen 
which collected upon its surface. In a later form of this cell, 
the anode portion was made nearly circular in shape, with a 
slotted opening of only a few inches in width at the top for the 
escape of the gases. 

While this process was first used for bleaching work, an 
experimental sewage disinfection plant was installed as Guilford, 
England, about 1904. This plant was investigated very thor- 
oughly by Dr. Rideal, and as a result of the experiments which 
he carried on he found "that 30 parts of available chlorine per 
million would reduce the number of bacteria in crude sewage 
from several millions to 50,000, while 50 parts would reduce the 
number to 20 per cubic centimeter. Colon bacilli were reduced 
from one million per cubic centimeter to less than one per cubic 
centimeter by 30 parts of chlorine. In septic effluent 25 to 44 
parts of chlorine per million reduced B. coli from 21/2 to 4 1/2 
million per cubic centimeter to less than one per cubic centimeter. 
With contact effluents smaller amounts of chlorine proved 
efficient. The primary effluent required 20 parts per million, the 
secondary effluent 10.6 parts per million and the tertiary effluent 
2.5 parts per million to reduce the number of B. coli so that this 
organism could not be isolated in 5 c.c." These results, par- 
ticularly as regards the removal of B. coli, were considered very 
satisfactory, inasmuch as a high degree of bacterial purity was 
obtained without the use of an excessive amount of chlorine. 

Notwithstanding the recorded success of these experiments 



DISINFECTION OF SEWAGE 133 

with the use of electrolytic chlorine, it does not appear that the 
so-called oxychloride process has as yet reached any considerable 
commercial development in England. This is undoubtedly to 
be explained by the scepticism concerning the disinfection of 
sewage by electrolytic chlorine which has existed in England since 
the failures of the Hermite and Woolf processes; also by the 
competition which bleaching powder offers in the way of a chlorine 
disinfecting agent. 

The Harris Process. — A plant employing the so-called " Harris 
Magneto-Electrolytic Process" for the disinfection of sewage, 
was installed in the city of Santa Monica, California, in the latter 
part of 1908. This process is in many respects similar to the one 
devised by Webster, which has been previously described. 
Certain additional features were introduced, however, such as 
the use of magnets, which were claimed to have an important 
bearing upon the successful working of the process. The use 
of these magnets has since been abandoned in the Santa Monica 
plant, and in the more recently installed plant at Oklahoma 
City, Oklahoma, which makes use of this process in a somewhat 
modified form, this magnet feature has been entirely omitted. 

The plant at Oklahoma City was placed in operation in March, 
1911. It is designed to treat 750,000 gallons of sewage per day, 
with certain guarantees as to the purity of the treated effluent 
and the yearly consumption of electrical energy. The guaran- 
tees which provide for the former are somewhat indefinite; while 
as regards the latter, it is stipulated that "the cost of electric 
current for operating the plant shall not exceed $750 per annum, 
provided that the cost of current shall not exceed 5 cents per 
K. W. hour." 

In this plant there are three treating flumes, each 18 in. X22 in. 
in cross-section and 30 ft. in length. In each of these flumes 
there are 10 sets of cast-iron electrode plates capped with copper, 
each set consisting of 27 plates, 3/16 in. XlO in. X24 in. Each 
flume is capable of treating 250,000 gallons of sewage in 24 
hours. Current to the amount of 270 amperes per flume is 
furnished by a 3 K. W. generator, which is driven by a 7 1/2 
H. P. A. C. motor, using commercial current at 220 volts. Of 
the 27 plates in each set, 14 alternates plates are connected to the 
positive terminal of the generator, while the remaining 13 plates 
are connected to the negative terminal. Baffles of sheet metal 
rest upon the bottom of the flume, and the sewage is forced to 



134 ENGINEERING FOR CENTRAL STATIONS 



flow between the parallel plates of opposite polarity. It is 
stated that " the sewage in the flumes becomes milky with minute 
bubbles generated by the current of 1 1/2 to 3 volts as it cuts 
the water into its two gases and liberates chlorine from the 
sewage." It is also claimed that "iron and copper are dis- 
solved and become powerful reagents and effective coagulents." 
The plant is stated to have cost $12,000, although the regular 
price for a plant of this capacity is ordinarily $15,000. Assuming 
an investment charge of $16,000 ($1,000 for the residence for 
attendants, and $15,000 as the price which any other city would 
be required to pay for a plant of this capacity), the yearly and 
unit costs for electrolytic treatment at this plant are estimated 
as follows: 1 





Per 
annum 


Per million 
gallons 


Per cent, 
of total 


Electric current 


$709.50 

660.00 

40.00 


$2.59 
2.41 
0.15 


28.2 

26.3 

1.6 


Attendance 

Lights 

Total operating 

Renewal of plates 


$1,409.50 
$200 . 00 


$5.15 56.1 
n 73 8.0 


Depreciation 

Interest at 5 per cent 

Total 


100.00 ! 0.37 4.0 

800.00 I 2.92 31.8 

1 1 


$2,509.50 1 9.17 100.0 

1 
i 



Use of Chloride of Lime, or Bleaching Powder, for the Disin- 
fection of Sewage. — As a result of the tests which were con- 
ducted at the Sewage Experiment Station of the Massachusetts 
Institute of Technology in Boston, together with those which 
were carried on at Red Bank, N. J. and at Baltimore, Md. in 
conjunction with the United States Geological Survey, it was 
found that, when three or four parts of available chlorine, in 
the form of chloride of lime, were applied to trickling filter 
effluents, it was possible to effect a removal of 95 per cent, or 
more of the bacteria in the effluent; also that 4 to 12 parts per 
million would effect a similar reduction in the bacteria in crude 

1 Engineering News, Vol. 67, p. 534. 



DISINFECTION OF SEWAGE 



135 



sewage, the amount of chlorine required varying with the quality 
of the sewage and the amount of oxidizable matter which it 
contained. As a result of these investigations, Prof. E. B. 
Phelps (Water Supply Paper 229, U. S. Geological Survey), has 
reached the conclusion that it is practicable to apply the chloride 
of lime treatment to the disinfection of sewage on a large scale, 
whenever the conditions are such that the disinfection of sewage 
is necessary or desirable, and he has presented the following 
table which shows the estimated cost per million gallons of dis- 
infecting sewage or an effluent with chloride of lime, based on a 
total daily capacity of 5 million gallons. 



Available 

chlorine in 

parts per 

million 


Time of 

contact in 

hours 


Cost per million gallons 


Storage 

tanks 


Other 

fixed 

charges 


Bleaching 
powder 


Labor 


Power 


Total 


1 


5.0 


$0.10 


$0.02 


$0.30 


$0.10 




$0.52 


2 


2.5 


.05 


.04 


.60 


.10 




.79 


3 


1.6 


.04 


.05 


.90 


.10 


.02 


1.11 


4 


1.2 .03 


.07 


1.20 


.10 


.02 


1.42 


5 


i 
.8 .03 


.08 


1.50 


.10 


.03 


1.74 


10 


.5 .02 


.16 


3.00 


.15 


.06 


3.39 


15 .5 .02 


.24 


4.50 


.20 


.09 


5.05 



In estimating the above costs, the price of bleaching powder 
has been assumed to be $24 per net ton delivered at the plant, 
and the amount of available chlorine in the bleaching powder 
has been taken at 33 per cent., which allows for a certain amount 
of unavoidable waste and deterioration. Labor has been com- 
puted at $2 per 8-hour day, with an allowance of 2 hours per 
day as representing the amount of care required by a 5,000,000 
gallon disinfecting plant using five parts or less of chlorine. For 
a greater number of parts of chlorine per million, the labor cost 
has been increased proportionately. Fixed charges, including 
interest, depreciation, etc., have been taken at 6 per cent, of the 
cost of the additional works required for the disinfection treat- 
ment. The fixed charges given under the item " storage tanks" 



136 ENGINEERING FOR CENTRAL STATIONS 

have been stated separately in view of the fact that, in many 
existing installations, sedimentation tanks are already available, 
and it would consequently be unnecessary to provide storage 
tanks for the treated sewage. 

From what has preceded, it should be evident that the dis- 
infection of sewage — particularly the disinfection of the effluent 
from a trickling filter or contact bed — is entirely practicable, 
provided complete sterilization as regards the pathogenic 
bacteria is not attempted. A removal of 95 per cent, and over 
of the bacteria — which, in the case of a trickling filter effluent, 
would mean a removal as regards the crude sewage of 98 per 
cent, or more — can be quite easily and economically effected, 
and this degree of sterilization should prove satisfactory in the 



b 




^ 


4C - 


it 


^ tx 


i 4L it 


« 3 it t\ 


s tX t, 


qzfT M /r 


1 L4 -, =_ V -L\ ~A 


s, M '- 7 W -*S^^7 v Z\ 


V £*- -W^ zV^V^r ^^ J 


1 zX Z \ j S^ ^£ t- 


— \/ r~~~\/ \ \ Z^ 


X^ ^" 


1 ^r 









Fig. 



1884 1886 1888 1890 1892 1894 189.6 1898 1900 1902 1904 1906 1908 1910 

26. — Showing maximum and minimum prices of bleaching powder in 
the New York market during the years 1883 to 1910, inclusive. 



great majority of cases. The amount of chlorine required, and 
consequently the cost of the treatment, increases very rapidly 
as the degree of sterilization is further increased, as has already 
been noted in connection with the German experiments with 
chloride of lime. As a result of these recent experiments with 
chloride of lime as a disinfecting agent, the City of Baltimore 
has decided to adopt this method of treatment as a finishing 
process, instead of using sand filters as was originally contem- 
plated. This change in plan will effect a saving of about 



DISINFECTION OF SEWAGE 137 

$1,000,000 in the initial cost of the purification plant. The New 
Jersey Sewage Commission has also decided to adopt the chloride 
of lime treatment for disinfecting the sewage of a number of 
seaboard towns which threaten shell-fish beds with contamination. 

Assuming that chlorine, in the form of a hypochlorite, is the 
most satisfactory disinfectant for treating sewage — an assump- 
tion which our present knowledge would seem to justify us in 
making — the future of electricity in the field of sewage disin- 
fection evidently depends upon the cost of producing electro- 
lytic chlorine as compared with the cost of chlorine in some 
cheap commercial form, such as chloride of lime, or bleaching 
powder, now provides. The maximum and minimum prices of 
bleaching powder in the New York market over a period of 
years are shown in Fig. 26. While these maximum and minimum 
prices have shown considerable variation from year to year, the 
general tendency of both has been downward, particularly since 
the advent of electrolytic "bleach." 

The Cost of Electrolytic Chlorine as Compared with Bleaching 
Powder. — As the cost of producing electrolytic chlorine is very 
largely dependent upon the energy efficiency of the electrolytic 
process employed, or in other words upon the number of kilowatt 
hours required to produce a given quantity of available chlorine, 
it will be necessary to consider briefly the question of electro- 
lytic cell efficiency in this connection. Before doing this, how- 
ever, the term " available chlorine" will be more definitely 
defined, as the relation of this quantity to the kilowatt hours 
consumed in the cell affords a measure of the efficiency of the 
electrolytic process from an energy standpoint. 

The term "available chlorine" is defined very clearly by Dr. 
Rideal, in his book entitled "Sewage" (1906), as follows: 

"'Available chlorine' means that portion of the whole chlorine which 
liberates oxygen on reaction with water. Hydrochloric acid and most 
chlorides liberate none. Free chlorine, for every molecule Cl 2 , or 71 parts 
by weight, sets free one atom, weighing 16 parts, of oxygen; C1 2 + H 2 = 
2HC1 + 0; that is, the weight of chlorine used is about four and a half times 
the oxygen obtained. Hypochlorous acid and hypochlorites break up 
directly into hydrochloric acid or chlorides and oxygen: 

HC10 = HCl + 

CA(ClO) 2 = CaCl 2 + 20 

NaC10 = NaCl + 
Hence pure hypochlorous acid, or a pure hypochlorite, would give one 
atom of oxygen for one of chlorine, or double the amount yielded by free 



138 ENGINEERING FOR CENTRAL STATIONS 

chlorine. Commercially, however, the hypochlorite is always obtained 
mixed with an equivalent amount of inert chloride, as in the formation of 
solutions of chloride of lime and chlorinated soda: 
2NAOH + Cl 2 = NaCl + NaCIO + H 2 
2Ca(OH) 2 + 2Cl 2 = CaCl 2 + Ca(C10) 2 + 2H 2 0. 
Therefore, apart from the question of difference of activity, the total amount 
of chlorine present in these chlorinated products bears the same relation to 
the oxygen yielded as it does in solutions of the free element." 

From the foregoing it will be seen that the available chlorine 
in a hypochlorite is really equivalent to twice its chlorine content, 
and in a sense, therefore, the term is a misnomer. It is, never- 
theless, a convenient expression and is one which has come into 
very general use. 

There are two general types of electrolytic processes, in both 
of which a solution of sodium chloride is electrolyzed with the 
liberation of chlorine at one electrode and caustic soda at the 
other. In one type these products are removed from the cell 
as soon as possible in order to prevent their recombination; in 
the other type they are permitted to recombine with the forma- 
tion of sodium hypochlorite and certain other compounds. The 
former process is used in the manufacture of caustic soda, where 
either diaphragm cells are used, or one of several methods is 
employed for removing the caustic soda from the cell as soon as 
it is formed. Examples of the other process may be observed 
in the cells of Hermite and Woolf; but it has been found that 
this process is considerably less efficient in the production of 
available chlorine than the one in which the products or decom- 
position are not allowed to recombine within the cell. One 
reason for this is that chlorates and perchlorates — both of which 
are practically worthless for bleaching and for disinfecting 
purposes — are formed simultaneously with the production of 
sodium hypochlorite, if the solution is hot or concentrated. 
Hence, by having the chlorine and caustic soda recombine out- 
side of the cell, this loss is largely averted. 

The electro-chemical equivalent of one ampere-hour is 1.32 
grm. of chlorine, and this is independent of the voltage which 
is employed. The minimum voltage required for the reaction 
involved in the electrolysis of a sodium chloride solution is 
approximately 2.3 volts. Therefore, 1.27 lb. of available chlorine 
per kilowatt hour represents an electr.cal efficiency of 100 per 
cent, on both a current and an energy basis. In practice, from 



DISINFECTION OF SEWAGE 139 

4.5 to 5 volts or more are required per cell, as a result of which 
the energy efficiency is reduced to approximately 50 per cent., 
even when the current efficiency is maintained at approximately 
100 per cent. This latter efficiency depends upon the design of 
the cell and, when there are no secondary reactions during the 
recombination, such as those mentioned above, it may be con- 
siderably above 90 per cent., although a current efficiency of 
under 90 per cent, is more common in.practice. A fair average 
energy efficiency for the later types of electrolytic cell is probably 
in the neighborbood of 45 per cent., which is equivalent to a 
production of a little over one-half of a pound of available 
chlorine per kilowatt hour. 

In a paper presented by Messrs. Phelps and Carpenter in 
1906, embodying the results of the early tests which were carried 
on at the Sewage Experiment Station at the Massachusetts 
Institute of Technology with chloride of lime as a disinfecting 
agent, the opinion was expressed that the cost of the treatment 
could be lessened by employing electrolytic chlorine produced 
at the disposal works instead of chloride of lime, or bleaching 
powder. Since then, however, as a result of further experi- 
ments which have been conducted by Prof. Phelps with electro- 
lytic cells, he has reached the conclusion that their use is not 
practicable in sewage disinfection work, due to the small differ- 
ence between the cost of commercial chlorine and the cost of its 
manufacture electrolytically. He states (Water Supply Paper 
229, U. S. Geological Survey) that "this condition is due to the 
fact that the demand for caustic soda is so much greater than 
that for chlorine that the chlorine is to a certain extent a by- 
product and can be made into bleaching powder and sold at 
low cost. On the other hand, the manufacture of small amounts 
of caustic liquor at the disposal works does not warrant the in- 
stallation of the necessary machinery for the production of pure 
caustic soda; consequently, without a market for this by-product, 
the cost of the chlorine would be the entire cost of operation. In 
addition, a skilled chemical engineer who would be required 
would increase the cost per million gallons more in a small plant 
than in a large one, and the uncertainty of the process and the 
increased responsibility on the sewage works both offset any 
slight advantage in cost which might appear in favor of the 
electrolytic plant. It has also been made clear in the present 
studies that the use of free chlorine as contemplated in the 



140 ENGINEERING FOR CENTRAL STATIONS 

earlier plan, is not economical and that some base should be 
provided for the preparation of hypochlorite. This base might 
be the caustic soda yielded by the process, or if a market for that 
by-product were available, lime could be used." 

Fig. 27 has been prepared to show the relation which the cost 
of the electrical energy required to produce sodium hypochlorite 
electrolytically at the sewage disposal works bears to the total 
cost of the chloride of lime, or bleaching powder, treatment in 
the case of a plant having a daily capacity of 5 million gallons 
per day. The daily costs of the latter treatment are those pre- 
pared by Prof. Phelps, as given in tabulated form upon page 135. 




3 5 7 9 11 13 

Parts of Available Chlorine per Million 

Fig. 27. 



The costs of electrical energy are based upon the use of an electro- 
lytic cell having an energy efficiency that would produce 1/2 lb. 
of available chlorine per K. W. hour. For any given number 
of parts of available chlorine per million gallons of sewage treated t 
the amount which may be expended per day for all other items 
of cost other than that of electrical energy, may be readily 
obtained from the curves in Fig. 27 for any given cost of electrical 
energy, on the basis that the total daily cost of the chloride of 
lime treatment is not to be exceeded. When consideration is 
given to the fact that the additional items of cost include fixed 
charges upon the investment in electrolytic cells and their 
appurtenances, the cost of a considerable amount of additional 
labor and superintendence, the cost of salt, etc., it will be 



DISINFECTION OF SEWAGE 141 

evident that sodium hypochlorite, produced electrolytically at the 
sewage disposal works, will find it difficult to compete successfully 
with commercial chloride of lime in a plant of this capacity. 
Moreover, the rates for electrical energy, as given in Fig. 27 are 
net, inasmuch as they are based upon a direct-current supply 
with the electrolytic cells connected in series. In the case of a 
central station which furnishes alternating current only, electrical 
energy would have to be sold at still lower rates than those 
shown in order to cover the unavoidable losses of conversion. 

In the case of larger plants, the costs would, of course, be 
more favorable to the electrolytic treatment, as the fixed charges 
and the cost of labor and superintendence would become materi- 
ally less per million gallons of sewage treated, but even in the 
case of large cities, it is questionable whether the saving effected 
by the electrolytic treatment would justify the municipal authori- 
ties in incurring the uncertainty and the added responsibility 
which would accompany the adoption of the electrolytic process. 
It is conceivable that some central stations, where the conditions 
would permit, might carry on the electrolytic process themselves 
and dispose of the resulting hypochlorite to the municipality 
for purposes of sewage disinfection. By this means, the cost of 
labor and superintendence could be reduced, and a higher price 
could be obtained for the electrical energy when sold in this way. 
Moreover, in the case of large central stations, it might be 
possible to derive an income from the sale of caustic soda, 
using lime as a base for the hypochlorite, and in this way further 
reduce the net cost of the electrolytic process; also in the case of 
seaboard towns and cities, where salt water would be available 
for purposes of electrolysis, the cost of the electrolytic treatment 
would be somewhat less than in inland communities where the 
purchase of salt would be necessary. 

While the costs of electrical energy as shown in Fig. 27 are 
based upon the use of a diaphragm cell for the production of the 
sodium hypochlorite, which is afterward applied to the sewage, 
there is no reason to believe that the electrolytic method of the 
Harris process, in which the sewage is subjected to electrolysis, 
as exemplified in the plants recently installed at Santa Monica 
and at Oklahoma City, is possessed of any higher efficiency 
from an energy standpoint. In the Harris process, chemical 
precipitation assists in the removal of the organic matter by 
sedimentation, but experience has shown that this organic 



142 ENGINEERING FOR CENTRAL STATIONS 

matter should be removed as a preliminary step to any process of 
disinfcetion, as otherwise a large part of the disinfecting agent 
will be consumed in the oxidization of the organic matter. 

While attempts have been made in many quarters to invest 
the electrolytic treatment of sewage with more or less mystery, 
the subject is in no sense a mysterious one. The electrical energy 
itself does not destroy or remove the bacteria and impurities 
from the sewage; it simply furnishes a means of producing a 
chemical reagent or reagents — usually in the form of hypo- 
chlorites — by the action of which the desired disinfection and 
purification are effected. Whether it is desirable to produce 
these reagents by electrolysis at the sewage disposal works, or 
to purchase the same or similar reagents in the market, is entirely 
a question of relative cost. If electrical energy can be obtained 
very cheaply, and if the freight rates on commercial hypochlorites 
are high, it would probably pay to produce hypochlorites at the 
sewage works electrolytic ally; where such conditions do not exist, 
the use of commercial hypochlorites will almost invariably show 
a saving at the present time. 



JUN 28 



1912 



